[Temen]

As stated, after Taps (lights out) a lot of recruits use that time to exercise. My division held push up, sit up, and sprint sessions for those recruits that weren't doing well on their PFAs. Also, I've seen plenty of recruits use the bars in the laundry room.
Granted, as previously said there are roving RDCs and you aren't supposed to be out of your rack. So, the risk is up to you. If you get caught, your whole division is likely to be ITed for a few hours. Not the best impression to leave on your fellow shipmates.
Also, Sunday mornings (I believe until 1300-1400) you have some "free time" in which you can write letters home, study, socialize, clean, etc. Just don't sleep. I'm not sure how impressed your RDCs will be if they see you exercising. I know they aren't allowed to IT you at all during your Sunday liberty, but I'm not sure about the rules for self PT. Again, to state that during P-Days you can't be PTed because you aren't "Fit for Full Duty", so I can understand the rule about no PTing without RDC supervision.
My best advice would be to make the PT sessions as difficult for yourself as possible. I know it won't be much, but just go as low as possible for push ups and hold it for a bit. Same as squats. When you do sit ups, always make your chest touch your legs (except for the PFAs).
I HIGHLY suggest you try being on the division staff. RPOC and AROC get beat for just about every mistake anyone in the division makes. As a Yeoman, I was beat every time someone failed to properly fill out the form that stated when recruits left the compartment (forgot what it is called), which happens all the time. Also, I was beat everytime someone entered the RDCs office incorrectly.