"It's spooky there and full of bad people." Harry nodded wisely. He loved ghost stories with Sirius but then he had to go to sleep. So usually it ended in tears and him lingering Sirius' room, wanting to share his bed for protection. Which caused all other issues.

"Don't worry about that. This place isn't. Look how nice it is." Remus used his wand and whispered - he would have opened the curtains but it was dark so why bother? "It's a bit late for him to be up."

Did Sirius grasp the concept of bed times? Probably not. He treated everyone, even young children, like adults.