I’m not sure I got the time change thing, maybe it’s me.
If the coroner stated at 9:23 am she was dead 9-12 hours, and the clock was set back already that morning, wasn’t the real time of the statement 10:23 am?
If so, the correct range for the death is 10:23pm-1:23am.

Also, now assuming the range 9:23-12:23 is correct: 2-4 hours earlier makes 5:23pm-10:23pm, taking into account all the possible combinations.
If so, Chery Jo could have had supper at a conventional hour (say, 8-9pm), after being at the library, in a possibly separate event.

Sunday, 30 October 1966, 02:00:00 clocks were turned backward 1 hour to
Sunday, 30 October 1966, 01:00:00 local standard time instead.

The autopsy was Monday October 31st 1966, so the 9:23 was calculated after the clocks had already been turned back, so no adjustment is required.

The workmen near Cheri’s car said they saw her, so that means they were aware of her and what she looked like. Given that, I can see two scenarios that might work:

She arrives before the library opens, checks out her books, and is out of the library by about 6:15.

Then
1. She runs into someone she knows, who wants to talk or go somewhere, so she puts her books in her car, rolls up the windows and locks it, then leaves with this friend. Sometime when she’s gone, someone else disables the car. Her friend brings her back to her car a few hours later, drops her off at her car. It’s hot inside the car, so she rolls down the window and tries to start it. It won’t start. Someone comes over to assist her, maybe suggesting she can call for help from another building. She goes into the alley and is killed. In this scenario, there would need to be at least 2 people involved – the friend she left with and the guy who disabled the car when she was gone. This is clear, because if the friend she left with wasn’t involved, he/she would’ve come forward to give that account.

2. She finds another location on campus to do some studying, where she works pretty much unnoticed, for a few hours. During this time, her killer sees her car, knows she will be returning to it eventually, and disables it. Cheri finishes her work, returns to the car, puts her books inside, rolls down the window, car doesn’t start, but someone comes along who offers to help. They end up in the alley, and etc. This scenario requires only one killer.

In either case, the car is disabled later, after the 4 workmen have left. I think Richard has a good point about that.

If Cheri figures out her car won’t start, immediately after she leaves the library, at 6:15 or so, she would’ve called for assistance at that time. Therefore, she probably didn’t discover her car wasn’t working until much later – much closer to the time she was killed – meaning it could’ve been tampered with at any time after the workmen, and other potential witnesses, had left the area.

Sunday, 30 October 1966, 02:00:00 clocks were turned backward 1 hour to
Sunday, 30 October 1966, 01:00:00 local standard time instead.

The autopsy was Monday October 31st 1966, so the 9:23 was calculated after the clocks had already been turned back, so no adjustment is required.

This confirms what I say, I think.
A coroner states 9 hours earlier, at 9:23 am.
Up to 2:00 am, it’s 7 hours earlier.
An additional hour passed between 1:00 and 2:00 am, because of the time change.
Another hour passed between 1:00 and 2:00 am, following the original time of October 30.
That’s 9 hours that point to 1:23 am of the original time of October 30.

If I’m mistaken, I don’t see it (honestly).

It’s a day and 7 hours earlier.

Clocks went back 02:00am on Sunday, October 30th.
It’s one day to 02:00am on Monday, October 31st.
Autopsy was performed at by Surgeon F. Rene Modglin at 09:23am on Monday, October 31st 1966

1:00 am to 2:00 am: 1 hour (time of October 30)

The clock is set back to 1:00 am

1:00 am to 2:00 am: 1 hour again (time of October 31st)

2:00 am to 9:00 am: 7 hours (time of October 31st)

That’s 9 hours.

Add 23 minutes, and you have 1:23 am, October 31th (time of October 30) as the limit of 9 hours stated by the coroner.
This puts the 12 hours limit at 10:23 pm.

So, according to the coroner the ranges proposed in the OP should be replaced with:

Time of death: 10:23 pm – 1:23 am
Time of meal: 6:23 pm – 11:23 pm

Yes, the time change kind of throw’s a monkey wrench into things and makes it a bit confusing,
makes me wonder if Dr. Modglin took this completely into account ?

"1. She runs into someone she knows, who wants to talk or go somewhere, so she puts her books in her car, rolls up the windows and locks it, then leaves with this friend. Sometime when she’s gone, someone else disables the car. Her friend brings her back to her car a few hours later, drops her off at her car. It’s hot inside the car, so she rolls down the window and tries to start it. It won’t start. Someone comes over to assist her, maybe suggesting she can call for help from another building. She goes into the alley and is killed. In this scenario, there would need to be at least 2 people involved – the friend she left with and the guy who disabled the car when she was gone. This is clear, because if the friend she left with wasn’t involved, he/she would’ve come forward to give that account."

It’s possible an innocent friend who dropped her off at her car (then left before she tried to start her car) could have
remained silent for fear the police might accuse him/her of being involved.

To me, there is almost no way she walks down that alley with someone she doesn’t know. It was terrifying from the pictures.
If he was offering a ride, it begs the questions of why she didn’t ask him to drive over to get her and why she didn’t take her books and why the car was left in disarray. If he pointed a weapon at her to get her out, why mess with the car engine?

The car ruse doesn’t work for me unless he’s disabled it after hours. It’s disabled precisely to get her to go down that alley. That doesn’t work unless the library is closed. If he’s done it earlier and she come out earlier and goes inside to get help someone realizes it’s been tampered with and the jig is up. If he intended to play the hero he would have “fixed” it for her for her gratitude and only blown his top when she wasn’t as grateful as he wanted her to be. He didn’t fix the car though. He wanted to do something to her in that alley.

1:00 am to 2:00 am: 1 hour (time of October 30)

The clock is set back to 1:00 am

1:00 am to 2:00 am: 1 hour again (time of October 31st)

2:00 am to 9:00 am: 7 hours (time of October 31st)

That’s 9 hours.

Add 23 minutes, and you have 1:23 am, October 31th (time of October 30) as the limit of 9 hours stated by the coroner.
This puts the 12 hours limit at 10:23 pm.

So, according to the coroner the ranges proposed in the OP should be replaced with:

Time of death: 10:23 pm – 1:23 am
Time of meal: 6:23 pm – 11:23 pm

1:00 am or 2:00 am on Sunday 30th, to 9:23 am on the 31st is over a day.

When the clocks were turned back to 1:00am on Sunday 30th, it was still 21 hrs 30 minutes before the screams in the alleyway, never mind another 11 hours until the autopsy.

To me, there is almost no way she walks down that alley with someone she doesn’t know. It was terrifying from the pictures.
If he was offering a ride, it begs the questions of why she didn’t ask him to drive over to get her and why she didn’t take her books and why the car was left in disarray. If he pointed a weapon at her to get her out, why mess with the car engine?

The car ruse doesn’t work for me unless he’s disabled it after hours. It’s disabled precisely to get her to go down that alley. That doesn’t work unless the library is closed. If he’s done it earlier and she come out earlier and goes inside to get help someone realizes it’s been tampered with and the jig is up. If he intended to play the hero he would have “fixed” it for her for her gratitude and only blown his top when she wasn’t as grateful as he wanted her to be. He didn’t fix the car though. He wanted to do something to her in that alley.

I agree, there is no way she leaves her car in the condition it was found, she was either forced into that alley
at gun point or some other force or she thought she was going to use the phone in one of those vacant houses.

I think the phone is most likely because her large tote bag purse was underneath her so it seems she was not under
duress until she got to the spot she was attacked. (maybe she was told there is a pay phone near the apartment
building on the corner of Magnolia and Terracina and they were headed in that direction)

When the clocks were turned back to 1:00am on Sunday 30th, it was still 21 hrs 30 minutes before the screams in the alleyway, never mind another 11 hours until the autopsy.

Sorry, Richard. Thanks for the clarification.
I was wrong by a whole day.

Anyway, I think that the meal time should be set to 5:23-10:23 pm, to account for the max possible range of 2-4 hours.

"1. She runs into someone she knows, who wants to talk or go somewhere, so she puts her books in her car, rolls up the windows and locks it, then leaves with this friend. Sometime when she’s gone, someone else disables the car. Her friend brings her back to her car a few hours later, drops her off at her car. It’s hot inside the car, so she rolls down the window and tries to start it. It won’t start. Someone comes over to assist her, maybe suggesting she can call for help from another building. She goes into the alley and is killed. In this scenario, there would need to be at least 2 people involved – the friend she left with and the guy who disabled the car when she was gone. This is clear, because if the friend she left with wasn’t involved, he/she would’ve come forward to give that account."

It’s possible an innocent friend who dropped her off at her car (then left before she tried to start her car) could have
remained silent for fear the police might accuse him/her of being involved.

If that was the case, I think that "innocent person" knew who the killer was, and was either afraid of him, or close enough to him that LE would’ve assumed he/she was a co-conspirator. Otherwise, why not tell LE what had happened? If Cheri went with somebody and that person simply dropped her off at her car and drove away, that wouldn’t be suspicious. And, if it was a friend whom Cheri would spend several hours with, that person would probably want to help the investigation and find out the truth about who killed her friend.

Unless, as stated, he/she knew who the killer was.

Importantly, she had "a supper type meal" in her stomach according to Richard’s site. Probably ate at home or brought something from home with her in her bag.

If it was someone she knew, then why the need for the ruse with the car? If she knew her killer, then she would be wouldn’t need a reason to go off with him. The distributor cap trick would be unnecessary. Seems more likely to me that it was a trick that a stranger would use and pretend to be a "knight in shining armor" offering to help.

If it was someone she knew, then why the need for the ruse with the car? If she knew her killer, then she would be wouldn’t need a reason to go off with him. The distributor cap trick would be unnecessary. Seems more likely to me that it was a trick that a stranger would use and pretend to be a "knight in shining armor" offering to help.

I agree, but in that scenario, why didn’t the person she went somewhere with ever come forward?

We have to account for the missing 3 hours – either she left the area or she remained there, somewhere, unnoticed. If she left, it wasn’t with her car, hence, it was with someone else.