It`s pretty simple:
If you play in a game, your vacation will automatically be scheduled to turn off in one hour. So make sure turning on vacation mode is the last thing you do before you leave. When returning from vacations, make sure you take all of your turns where you're over the boot time within one hour of each other.
You must leave all ladders before turning on vacation mode. If you re-join the ladder, your vacation will automatically scheduled to turn off in one hour, just as if you played in a game.