Airplanes behave just like trains, they stop whereever they are for one hour until time catches up with them.
My wife and I would routinely spend a week in Hawaii from LA ending with the april time changeover.
Outbound we only had a 2 hr adjustment and since we always took the redeyes home we ending up usually leaving 3-45 minutes early and the airlines would be very clear in the announcement. TWA it was, used the L1011 for the 8a LAX-JFK departure and thus NEEDED the plane back in LA by 7a to turn it - so they changed the departure time of this flight and told people it would leave at that time and no later.
It was nice, we needed to deal with travel shock and instead of doing the DST travel shock we did it all in one fell swoop with 3 hours instead of 2, and we left earlier at night and got in usually Sunday early, had the whole day to adjust and bingo we are back on west coast time and over the jet lag all at the same time.
It also worked out that the L1011 had nice sleeper seats in F class and F class cost about the same as mildly restricted coach back then - they wanted to fill the plane and we earned tons of miles to the point that we are both million milers now in the AA program and permanently ‘Gold.’