Phase

 PHASE (of people) 1. n. The phase of one's waking-sleeping schedule
       with respect to the standard 24-hour cycle. This is a useful concept
       among people who often work at night according to no fixed schedule.
       It is not uncommon to change one's phase by as much as six hours/day
       on a regular basis. "What's your phase?" "I've been
       getting in about 8 PM lately, but I'm going to work around to the day
       schedule by Friday." A person who is roughly 12 hours out of
       phase is sometimes said to be in "night mode". (The term
       "day mode" is also used, but less frequently.) 2. CHANGE
       PHASE THE HARD WAY: To stay awake for a very long time in order to get
       into a different phase. 3. CHANGE PHASE THE EASY WAY: To stay asleep
       etc.