How long is preschool during the day?

-Like, how long do the children stay in preschool before the parents come to pick them up?

For United States, I mean...Usually preschool is half day. 4 hrs either in the morning our afternoon 8 ta noon and 1 to 4 were my child's hours. If u are late picking your kid up they can call the police.My nephews is from 8-2 and they have nap.