i'm doing the premium membership trial, and i cannot for the life of me figure out how to do it...
lol. I had the same problem. =:0)
You go to your settings (on the bar at the top) and on the left menu there is a choice called "Vacation"
Go there, enter you start and finish dates and the server does the rest.
*Be sure to take all your turns before ending/cancelling your vacation*
otherwise you'll end it and get booted from all your games.