Worrying about coming up short is probably the most stressful...or getting held up, depending what kinda area you live in...
Plus you're only working 4 hrs? That shouldn't be that bad...
8 hours. But before 8 we usually have 3 people in the store. And it's technically more as we're expected to finish our work but, due to customer volume and a lack of employee's we never finish by 12:30. We usually don't get to leave till 1, have to leave multiple things undone, and get lip for it the following morning. I estimate that, if we actually 'finished' everything we'd be there until 2 A.M. It's just not possible to get it done any sooner with the number of customers we have before closing.
You said in the OP 8pm to 12 midnight...unless you meant 12 Noon then that would be 16 Hrs...