Why does the hours say 8am-10pm but they close and lock the doors at 9:30pm everyday?

We close early at 9:30 because those are our new hours. They didn't send us a new store hours sign schedule yet & can't make our own. We are short staffed. Everyday we have one person which is me stocking the shelves for the night shift then we have the assistant manager then we have one cashier. All 3 of us are doing 10 job's at once & we only get paid $13.20/hr to do the job we got hired for. He's not a pain, he can only do something much & the store manager isn't much of help at all.

The night manager. It's the biggest pain ever.