In general if you show up before your assigned time you will stand with your group and then will be allowed in at the designated time, then go through the security line and enter the sight. This is especially true at the Accademia which has multiple roped off lines for every time and it runs like clockwork.
It can be a strategy to so up five or ten minutes after your start time and try to skip some standing around but you can't skip the security line which is most the wait since the entry to show and/or scan your ticket takes only a few seconds a person. I think most people are more worried about missing it so they end up 15 minutes early to make sure and then just stand with their group.
I know previously (2022) if you purchased some tickets like the PassePartout ticket you had to redeem it in person at the ticket office before going into the Uffizi but I think that may have done away with that step and gone with scannable tickets.
Keep in mind that these places handle these crowds everyday and they have it down. Signage is usually pretty good if you keep your eyes open and there are also generally people managing the lines and pre-checking that people are in the right line for their tickets to speed entry.
Enjoy Florence,
=Tod