I'm so surprised that many FAs actually allow early boardings. In our manual, it states exactly when boarding is to occur.

Report times for FAs to aircraft:
737/S80 - report to A/C 40 minutes prior to departure

757/767/777 - report to A/C 50 minutes prior to departure

Agents cannot board until Minimum crew is on board.

This allows FAs 10 minutes before pax boarding to check emergency equipment, (hopefully) check catering, and have a crew (pilot/FA) briefing before pax boarding.

Pax Boarding:
737/S80
Begin boarding no later than 30 minutes prior to departure

757/767/777
Begin boarding no later than 40 minutes prior to departure

For some International destinations, boarding begins 40 minutes prior to departure.

Reading this same issue on FA FB sites, and FAs are upset that agents are trying to push for earlier boarding, due to full flights, 'x' amount of wheelchairs/pre-boards, but FAs are pushing back because it's too stressful not only for us to check everything quickly and have a quick briefing, but most importantly, you the pax when it's more chaotic.

Of course, this sorta changes a little during Irrops