IMO - doing one of the two:
1) cardio
2) keeping cals low
is probably OK on a bulking cycle (although i wouldnt do it personally). either one will most certainly hinder gains (especially #2) but you'll still make some gains....HOWEVER: doing BOTH is almost asking to add virtually no muscle mass. 20 minutes a day on ~2500? cals - with what is your body supposed to use to put on muscle? here are a couple arguments:
hormones are not to be taken lightly. they tamper with a very sensitive chemical system and can have far-reaching negative impacts if not used properly. if i could accomplish through diet what i can with PH, i would just use diet. i can put on 5lbs in 6 weeks using absolutely perfect diet and non-hormonal substances, but thats about it, and i will lose those pounds if i dont keep that diet absolutely perfect (ever tried this? eat like an absolute champ for a month and watch the muscle pack on, only to be lost if you return to previous, maintainable diet?). PH use puts on pounds that, if done right, dont go away even with simple caloric maintenance (still high of course) and contrary to caloric increases: when the cycle is over, you will NOT be fatter than when you started (this is through diet manipluation - something many fail to do properly and end up a little fatter, necessitating cutting cycles) if you look at guys who have juiced in the past - many of them are STILL muscular, even if their diets go to ****.
anyway, that's why i say to extract the most possible result from a PH cycle. you only get to do a few of them (unless you stock up) and the fat/water lbs you put on will come off very easily. if you're gonna spend the money and take the time and the risk: maximize the benefit, and also go with what works.