From what I can tell, law enforcement or Homeland Security or anyone else with the proper warrants can get extremely detailed "real time" information from someone's cell phone provider. What is not so clear is what information can a Cell Phone provider obtain about past activity when the phone was not being monitored. Certainly they can furnish the time and cell tower(s) used for any incoming or outgoing call. What I can not verify is whether or not the cell phone provider can obtain a record of what towers a phone that was "on" but not in use had "pinged" off of and can they tell the exact time the phone was powered off (or out of range, had its battery removed etc).
I went back to the case of Adnan Syed as documented by the podcast "Serial". The Cell Record of where he was ( or more correctly, what cell tower was used) when each incoming or outgoing call was made was the primary evidence used against him. The record of what towers his phone was pinging off of when he was not using it would have been invaluable but that information was not introduced. I would assume because it wasn't available. I am not sure his phone was ever powered off so I don't know about that information.
If Jennifer's phone was actually powered off a or around 10:40, it comes very close to certainty that the action was related to her disappearance. There is the small chance that she powered off because she was angry at her boyfriend but this would be an unusually irresponsible act on her part.
If the phone was just not used after that time, it doen't tell us much of anything.
It may depend on the service used. Different companies maintain different records. Also what towers they either leased or owned, at that time, can factor in. How the antennas were configured.
There are a lot of variables.
Because LE appears to have gotten phone records somewhat quickly, after JK went missing, these records probably do contain a great deal of info.
Even predictable people can do unpredictable things. More so than the JK's phone pinging or not pinging after 10:40 PM, I wonder about the mace left on the kitchen counter.
She always carried mace, yet it wasn't taken with her that day. Was there just not enough room in her purse, or was she not on her game that morning? Distracted? Or was there a knock on her door early that morning, that because it was morning, she might not have been afraid to answer?
I don't know if the mace being left behind, points more to a night abduction, but it's one of the first things that her mother reports was concerning to her.