Rabbits tend to be most active around dawn and dusk (hence they're called "crepuscular"), but that doesn't mean that they are wide awake during that time and sleep solidly the rest of the time. They'll tend to nap from time to time during their "awake" periods, and be active from time to time when they're supposed to be "asleep".
Because many rabbits sleep with their eyes open, at least partially, it's often difficult to tell if they're asleep or not - Natasha's nose twitches less when she sleeps, and her eyes half close, even mostly closed sometimes. Scone was much the same, except I don't think I ever saw him with his eyes fully closed.
Natasha usually becomes active at the first light of dawn, although she's learned that I don't appreciate her picking that time to start grooming my head. She'll wait until the earlier of my alarm going off or her getting hungry (usually 8:00AM or thereabouts), and then if I'm not up she's in bed reminding me that I live with a rabbit, and it's time the rabbit was fed. If I'm home all day, I've noticed that she usually disappears around 10:30 in the morning, then reappears around 2:00PM to see where I am and what I'm doing. After a little reassurance, she disappears again until about 5:00PM when it's time to remind Dad about the whole dinner thing. At 10:30PM, like clockwork, she runs into her cage for a bedtime snack. She'll usually come into bed with me as soon as she's done with the snack, kiss my hands for a while, then hop off to the foot of the bed to take a nap. Overnight, she's usually in bed with me or lying down on her fleece next to the bed, or chewing on a toy.