I've always had success keeping my diet practically the same for 5-6 weeks after PCT. Your body needs to adjust to your new size, it's first instinct when you come off of gear will be to reject the new size. So it's very important to fuel the new size with lots of calories and lots of protein. After I finish a bulking cycle, diet wise, I always consider post cycle therapy and 5 or 6 weeks after as a phase 2 of the cycle. Once your body has adjusted in that time frame, you can gradually taper down. But don't shock yourself by quitting the same diet or you may find yourself sacrificing your hard earned gains.
P.S. like mentioned above, make sure that they are clean calories and clean foods that your eating.