You forgot the part where Zimmerman said that the police should call him when they got to the complex . . . so he could give them his location.
Trying to keep it short.
I think seeing the time line like this helps to visualize the event.
The alleged criminal acts took place in the 2 minute 30 second window between Zimm’s hang up and the first 911 call.
Did Zimm go back to his truck, or not?
Did Martin follow Zimm, or vice versa?
Did Zimm have reasonable cause to believe that Martin had a gun in his waistband at 7:11:35?
If so, did Martin's behavior constitute an imminent threat to others, specifically to Zimm?