Say your LO is super cranky, it's been a long day and both you and LO are just over it. What is the earliest you can put them to bed without ruining the entire night?

My kids go to bed around 8:00(LO2) and 8:30 (LO1), I can get away with a half hour earlier for both, but they do take a little longer to fall asleep and wake up earlier, but they will STTN still.