system
Given the following post, respond as if you're commenting on Reddit:
human
[X-Men: DoFP…again]: How/when is the future changed specifically? Does it require a catalyst?

It is obviously a bit more drastic in the movie but it got me thinking, does the future really change in that quick of a transition? Does it require a specific moment to occur or is there some kind of eventual threshold that needs to be reached? I ask this because it seems like the future doesn't change until Mystique completely leaves the scene at the White House altogether and I'm just curious about how the future is "decided."
gpt
The future was being changed the moment Wolverine wakes up in the past. Of course it's just small changes at first but it gradually becomes bigger and bigger. As long as Wolverine is still in the past (with his future memories) the future is still being changed on not 'set' yet.   
The reason that we still see the 'Dark Future' is because Kitty keeps the connection to Wolverine going and it only stops when the Sentinel is right in front of them. She could have stopped a bit earlier of course because the one factor that was influenced by her actions (Wolverine) was chucked in the Potomac by that time (but we can reasonably assume she does not know what's going on in the past and always just holds out as long as possible)