Agreed. However, there are times when I get a little too much sleep (>10 hours) and feel like crap for the day. I do however notice a direct corellation between how much time I spend doing productive stuff and the amount of sleep I get. If I get between 6 and 9 hours of sleep, I am feeling and perform my best. If I get less, I generally feel scattered and off. If I get more, I am lethargic. I have had longer naps (~3 hours) during the day for periods when I am up late working on prejects and I find this is a bad cycle to get into as waking up from these naps is pretty muc impossible. Getting up once each day is hard enough!

I have read that REM cycles work in 3 hour cycles and a 9 hour sleep would run 3 cycles. That is why it is sometimes recommended that people sleep in 3 hour cycles. I would think though that each successive REM cycle is more effective and restful than the previous leading to think that 3 successive cycles is better than two during the night and one during the day. I am no expert though and just going by things I have read and heard on the matter. I would just say sleep just during the night.