This is sort of a stretch that attempts to unite in- and out-of-universe explanations:
The sequence of events presented in the final edit don't necessarily represent the in-universe events. Perhaps days elapsed between Grissom
's arrival at Genesis and Sarek's arrival in San Francisco. Maybe we were shown the events on Genesis pre-Enterprise
as flashbacks? Once the Enterprise
arrives both stories catch up to the "present". (I know this is probably not what the editors intended but it kinda works!)
By the way, this whole thread is a good catch! I never noticed this. You may have ruined this movie for me! LOL. But I just learned about the last minute editing changes, so it's been interesting.