Quote Originally Posted by Anteros View Post
There was already an alternate timeline anyway. Cap didn't create one. From the moment they knocked out Star-Lord or let Loki escape or did any other thing that changed the past, the timeline split already. Cap just went back to the already split timeline and lived there. He didn't doom anyone. If anything he probably worked to stop Thanos from ever becoming a threat in that timeline in the first place, ultimately saving two timelines.
As I understood the Bruce/Ancient One conversation, the idea that they could return to the exact point the stone was stolen, return it, and use the Time Stone to smooth things over, thereby not splitting the timeline.

The events in New York do present a problem for that, but for at least four of the stones, this should work fine.