My nearly 4 yo DD is a shocker if she gets overtired so is in bed by 6:30 most nights. Last night was 5:45. Regardless of when she goes to bed she is alway up by 6:30am. I tried making bedtime 7:30-8ish thinking she'd sleep in but no luck.
She seems to get a superpower when overtired and bounces off walls whilst giggling and mucking up until she passes out...which is no fun for anyone.