Ball park figure
- Generally speaking, most people will be able to withstand 3-4 hours of workshop in one day.
- If you are really new to belly dance, maybe 2 hours will be enough.
- If you are an advanced dancer, 6 hours should be doable.
What it will really boil down to is your general stamina/physical shape. The better in shape you are, the more you'll be able to do (again, ball park figure). If you don't practice much outside of your classes and don't do much physical activity outside of that, stay within that 3-4 hours per day... or else you may have major muscle aches.
Festivals vs. 1-2 days workshops
Again, generally speaking, that 3-4 hours per day should be doable whether you do 1 or 2 days of workshops (so Saturday only vs. all weekend types). When we're talking multiple days festivals (e.g., Tribal Revolution, 3rd Coast Tribal, Tribal Fest), then you may want to consider your general physical shape again. You will hit a wall at some point and you ideally want for that wall to hit after you're done with workshops.
In the 3rd Coast Tribal 2011 edition, I overdid it: 5 hours on Thursday, 6 hours on Friday, 4 hours on Saturday, and 2 hours on Sunday. Well, I had a hard time walking right on Saturday after the workshop and I had to perform that night. I did manage to get my limbs to cooperate again and all was fine. But, yeah, hit that wall.
The first time that I did a lot of dancing was for the Golden Opportunity intensive with Ariellah and Rachel Brice in 2008. I had prepared myself ahead of time but it was still not exactly enough. We had 3 hours with Rachel in the morning and 3 hours with Ariellah in the afternoon. I was hurting A LOT on the Saturday as well. But once you go beyond that wall (in that case on Sunday), you can do stuff more normally (yes, like walk and lift arms :p).
Instructor and topic
Some instructors are hardcore drilling mavens and you know that 2 hours with them will be harder than, say, another instructor who will talk about concepts or go easy on the drilling. So keep that in mind too.
In terms of topic, well, there's a whole gamut, obviously. Something on artistry will generally have a lot of introspection and exercises won't be about flawless dancing so easier on the body (but harder for the brain; see below). Veil workshops will kill your shoulders. Sword workshops will kill your head (and may create a whole lot of tension in your body). Bhangra/Bollywood workshops will kill just about everything in your body. So do slow and slinky workshops. ;) But you catch my drift. Keep the topics in mind as well and see whether you would be overworking the same area on the same day.
Pace yourself DURING the workshop
In general, it's always a good idea of pacing yourself during the workshop as well. I wrote something about that a while back. Given that I was really bad in phys-ed when I was a child/teenager, I knew when to stop. It's easy for me to figure that spot. I'm not encouraging you to slack off but rather to know your limits and not go beyond them.
Also, knowing the workshops that you have coming up, you may want to do less in a certain workshop to keep your energies for the next one (or for performing). That will be highly dependent on your schedule, obviously, and where your priorities lie. But I've heard countless times people whine "I was really wanting to take XX workshop but, when I got it, I was so tired from YY workshop, that I don't remember any of XX." So you don't want to do that, obviously.
When booking your workshops, also consider the amount of recovery time that you may need. For some festivals, workshops are back to back because they expect folks to spread their time. If you can do all those hours in a row, go for it. If you need recovery time, do plan for it. I generally like 1-2 hours in-between workshops but it's not always doable.
Think about your mental fatigue as well
Right now, I've focused more on the physical aspect but, lemme tell you, your mental will take a toll too! There's only so much material that you can absorb in one day (or over a festival)! At the Golden Opportunity again, on the Saturday morning, while I could still physically dance, I couldn't absorb the choreo/combos that Rachel was teaching... but I was still dancing on the sideline. I just couldn't absorb new material. So take that into account as well when booking your workshops.
It's not a contest
It's important to remember that it's really not a contest: no price is awarded to the person who dances the most. Really. What is most important is that you come out of the workshops with material and a good experience. So if that means that only 2-3 hours per day is what you can do, there's absolutely no shame in it. It's actually more shameful to overbook yourself and not remember any of what you learned. So do pace yourself when booking yourself for workshops. And, heck, consider practicing more at home to build your stamina if you feel like you want to do more. ;)