I feel like beyond basics like breaks, "an Equity rehearsal" can vary wildly depending on the contract. On some smaller contracts you have to have the whole rehearsal schedule announced at the beginning of rehearsals, and other larger contracts, as long as you stay within in your weekly and daily hours you can give 12 hours notice of what rehearsal will be.
Working AEA style you cannot call the entire company for every rehearsal and then figure out what you're going to do with them once they arrive. The schedule needs to be set well in advance and specific calls need to be provided.
Yes and no. You probably
shouldn't call the entire company for every rehearsal and then figure out what you're going to do with them (makes everyone really cranky), but you can as long as you're within your hours. Particularly in tech, I've definitely put out schedules that call FULL COMPANY for WORK TBA.
My university also had an AEA based rehearsal rulebook, that everyone had to sign at the beginning of rehearsals. We followed the AEA break schedule, and we even had a deputy of sorts.
Some of the biggest differences I can think of in an AEA setting, as others have pointed out, pertain to the media rules. They are another thing that differ from contract to contract, and its the section that changes the most with every renegotiation as theatres and the union come to terms with the changing role of the internet/youtube/twitter, etc. in our industry.