Not at all hard, Id simply fall asleep as soon as I got home from school and wake up at the time everyoen in the house was going to bed, then Id stay up all night. I was "nocturnal" for a week, and now back on a normal sleeping schedule I havent had problem sleeping since!
To get to sleep on time the first day of my nocturnal week I simply didnt sleep the night before.
some/most of you probably cant call it a day at 3-4pm though.