Why am I so tired?

I don’t get this, if I go to bed at 5am and wake up at 11am that is only 6 hours of sleep and with a cup of coffee I’m bright eyed and bushy tailed ready to start the day. But if I go to bed at 3am and wake up at 9am (still only 6 hours of sleep) it doesn’t matter how many cups of coffee I have I’m still tired and fighting to keep my eyes open. Why is that? I’m still getting the same amount of sleep either way.