The store doors have closed. But before you could go out, the employee walks out and closes the last door. You are the only one in the grocery shop, probably. There are no zombies but you would need to wait until about 6 AM to exit the store. You will need to eat and craft stuff in the mean time to survive inside the grocery store. The grocery store will get loaded at about 5 AM, but the truck drivers will most likely never step inside the grocery store and help you out.