I have an evening reservation for after work, but I may be able to go during the work day. I wonder if they would take me that many hours early or if I can change my appointment.
On launch day almost certainly not. There are no more appointments available for launch day and they only take a certain number of people every 15 minutes. If you show up more than 15 or maybe 30 minutes early they will tell you to come back at your appointment time, especially if your store is a very busy one.
However, it is worth noting that they do allow you to come any time after your appointment window for up to two weeks. So in the future the best plan is to get an early appointment. If you can make it, great, but if you have to go after work, that’s fine too.