I stopped covering my bird because it was my way of giving him "timeout" when he was naughty. He's learnt that if he's mouthy, he gets 3 verbal warnings then the sheet for 10 minutes. I just dim the lights in the evening as I can be up until the early hours working, as i am now. Some birds will slowly get used to your routine & go to sleep in thier own time given subdued light & quiet.
My Eddie seems to like 8hrs of sleep, like me, and even if the curtains get left open in the morning, if it's not been 8hrs he'll still have his wee head tucked under a wing, fast asleep bless him. Routine is just as important to a bird as anything else, though everybody else has different views on it & different natured birds.