Question is in the tilte i'm a student and i will be at school when it end so i was wondering

I'm guessing it's like any other jam where you could submit at any time. They're just trying to say "don't work until the very end, leave some time to submit so we don't have to deal with people submitting late."

Submit at any time. The 30 minutes is an extra buffer period exclusively meant for submitting if you didn't get to it by that point.