It's your time... like in real chess; if you leave yourself with insufficient time to make a number of moves before time control, you only have yourself to blame!
Ending vacation without losing games?

Plan all your moves and blitz them? But I'm almost certain time will be added to your clock as soon as you get back from vacation, seeing as it deducts multiples of 24 hours from your vacation time and adds the remaining unused vacation time onto your clock when you come back.
Just play, you should be fine.
I'm ashamed to admit that I completely forgot about my online games on chess.com for about a week. Thankfully, auto-vacation kicked in, but now I have multiple games with "a few seconds" left. How can I make a move in each of them after ending vacation before they start to auto-lose?