David Accedemia gallery entry

I would say no: there's a reason why they issue reservations by time slot, and my guess is that they'd be more apt to let people who've patiently stood in the ticket line (should there be a queue at that time) in before an entry-time jumper. I guess you could try it but I wouldn't bet on it?

If it's a busy day, you will not be allowed in early. I have seen people turned away several times.

The appointment time is to help maintain a number of people going in at the same time.

We made it in an hour early no problem.

Well never say never, I guess! :O)