I'd say its anybody's guess. Many have assumed (myself included) that the time of TM running into the the "gated place" and taking shelter at the "mail thingy" corresponds with the start of the 6:54 call which lasted 18 minutes, ending at 7:12 which is when TM "ran" from GZ. However, if you look at her testimony, Dee Dee says that when TM was about to leave the shelter to start walking, the phone hung up and she called him back. If we trust her recollection of when the phone hung up and it being tied to an event (phone hung up when TM ran for shelter, phone hung up as he started walking from under shelter, phone hung up when TM ran from GZ), then the phone hanging up when he was about to leave shelter and start walking would have to coincide with the start of the 6:54 call and that would put TM running for shelter at an earlier call that got disconnected.
Personally, I don't think we can use Dee Dee's testimony to establish much of a timeline of where TM was and when as her description of calls hanging up and what was happening at the time doesn't seem to fit. I'm not suggesting she is making stuff up, but that her recollection, like most witnesses isn't exact.
One question about the cellphone records. This may have been discussed here before, but I was reading at another site about how T Mobile shows times/length of calls on there bills. They said if a call started at 7:11:59 and ended at 7:12:01, the bill would show this as a 2 minute call that started at 7:11. Is this correct? If true, this would mean that Dee Dee's last call would have started between 7:11:00 and 7:11:59 and ended between 7:15:01 and 7:15:59. We know that seconds haven't been provided to us, but is second component of when a call started/ended available from TMobile?