The benefit to taking DNP during the summer is that most people are running their air conditioning. You also don't look like you're insane when you have a big fan pointed at your head. If you're going to be outdoors a lot, however, then you'll want to run a low dose of DNP. You can definitely take DNP in the summer. Just make sure the dose is appropriate to the circumstances. You may find that only 100-200mg/day is compatible with your circumstances.
As for taking it during PCT, I think that's a terrible time to be using DNP. Some have theorized that it's a good time since they think that DNP lowers thyroid levels, and thyroid is catabolic. This reasoning is questionable though. First, DNP doesn't appear to impair thyroid function. It's often stated as fact, but it's very poorly substantiated and real world bloodwork calls it into question. Second, it's not clear that lowering thyroid levels below normal is anticatabolic in the first place. Sure, raising thyroid levels is catabolic, but the oppostive is not necessarily true when you're lowering levels below normal.
The drawbacks to taking DNP during PCT seem pretty obvious to me. The whole purpose of PCT is to restore testicular function and to maintain muscle mass and strength. I think that DNP would interfere with both. PCT is NOT the time to be dieting, depleting glycogen, and reducing muscular performance. My recommendation is to run PCT at maintenance calories or even a few 100 calories over maintenance. This will give you a nice anabolic environment as your test levels return to normal. Keep lifting heavy in the gym. Once PCT is over (4-6+ weeks after your cycle ends), THEN start dieting and bust out the DNP. With testosterone levels restored to normal, muscle loss will be less likely. I think it makes much more sense to take DNP (and to diet) in a recovered, post-PCT state.
Hope that helps,
Conciliator