Thanks for your reply
When I did monophasic sleep, I tried to go in bed at 10 PM to sleep 8.5 hours, but because of my homework I often stayed up until midnight, so that makes 6.5 hours of sleep (but I was really tired in the mornings, couldn't get up without 3 different alarms, etc...). Now I have a lot less problems waking up, so I think biphasic sleep is much more better, refreshing, etc.. for me.