I have found that it is not the time duration of sleep, but the waking up time that is important in my productivity. If I wake up at 11 in the morning after 4

I have found that it is not the time duration of sleep, but the waking up time that is important in my productivity. If I wake up at 11 in the morning after 4 hours of sleep, I am much more energetic than after 7 hours of sleep if I wake up at 5 or 6 in the morning. If I sleep less, of course I feel sleepy sooner in the evening. But never have had energy issues. OTOH, 8-8.5 hours of sleep anytime is optimal for my energy. I have seen that I am outright miserable after 6 hours of sleep and waking up at 6 although I am fully productive after 4 hours and waking up at 11.