I like a few hours for me, before I go in to work. Some days I sleep a little late, and have only an hour or two. At least twice a week, I set the clock and get up very early.
I have noticed differences in my mood and energy level.
On those days when I get up earlier, I am actually able to do the things I want to do. On those days where I sleep later, I am only able to wake up for work, and not always successfully - sometimes I remain sleepy all day.