Tonight. Officially, at 2:00 AM you set it ahead to 3:00 AM. Just do it before you go to sleep.
I try to do all the clocks ahead of time, then set my bedside clock, just before turning in. I'll do the car clock in the morning; it's a tricky one.
You can do it whenever you want, but most in most States time keeping skips forward at 2:00am.
(excsept Arizona, Navajo territories, and Hawaii which do not observe DST)
