I've had two PEBs.
The first was in the immediate aftermath of my cancer. If I understand it correctly, because I was "medevac'ed" to a base for the diagnosis, treatment, and IDES process (meaning I wasn't assigned to a unit there) my day-to-day *could* have been doing minimal work as an extra body in the clinic as part of the one-man "patient squadron".
What actually happened is I got bored and started "volunteering" full time at the base squadron where folks with my AFSC normally work. They allowed me to work as much as I was able, which quickly turned into a standard full-time schedule. This was good, because my case started with discovering a tumor in March 2009 and the IPEB decision didn't come down until August 2011. That could have been a LOT of time spent milling about in the clinic.
The second one, which I'm currently undergoing, is for the pulmonary fibrosis that was caused by my cancer treatments in 2009, but not noticed and diagnosed until 2015. (Late-onset side effects are one of the little adventures you get to deal with after beating cancer.) For the most part, I'm working an ordinary schedule. But my duties are all kinds of goofy because I was passed over for promotion (partially as a result of my previous PEB experience) before the MEB was initiated, so I'd already been moved out of my regular squadron and into positions that were supposed to afford me better visibility with the higher-ups.
So, while I'm still working full days, I'm not doing what would be considered my normal duties. In fact, I'm currently working in a Wing Staff Agency position that's supposed to be a civilian but was unfilled because we haven't been able to hire a new one for over half a year.
Regarding PT: For my first one, I was exempt for all events. I don't know if that was because of the medical issue, being assigned to the patient squadron, having the "Patient" AFSC, or what, but I didn't take a test for that whole March '09 - August '11 timeframe.
For my current one, I'm just exempt from the cardiovascular event because my lungs are the problem. But I'm still on the hook for waist, sit-ups, and push-ups.