My core sleeps show me I'm still in the adaptation phase: even though I sleep for 4.5 hours and have a lot less problems waking up (compared to my monophasic schedule), I spend 10 minutes in bed, just laying around. And I keep yawning for the next 20 minutes, and feel good after I take a shower. I have no problems of concentration during the day, it's not working so bad after all. But I hope I'll really be efficient and never tired when I wake up, like other biphasic sleeper say they do.
I think I'm addicted now: I woke up 30 minutes before the end of the cycle because of my sister, and couldn't stop myself from yawning for the next hour. Anyway, today is friday night, and I'll try to have a 7.5 hour core sleep (maximum).