I assume the end call time was that garnered from TM's phone call. I presume we have no idea whether he hung it up or it hung up on its own (W8 describes it going dead at some point, not that TM ended the call). Looking for clarification is twofold. The more W8 testifies to hearing, the less gap there is between the time GZ ended his NEN call and the two encounter each other. If she heard nothing, then there is a 2 minute gap, but if she heard as much as indicated in the BDLR/Crump interviews, it might only be a 90 second gap. IT may also call into question either the narrative of W8 or that of Jenna/Jeremy. W8 says she heard verbal exchange and some scuffling, but no cries for help from anyone, so lets presume she heard 20-30 seconds of the encounter. This would mean it was at least 45 seconds from the time Jenna heard the start of the verbal exchange until she called 911, which is longer than they describe.
We aren't talking about huge gaps of time, so certainly within the margin for error of guestimates after the fact. I think its certainly possible W8 hear argument and Jenna/Jeremy heard what they did and have them fit within the timeline.