I intended to keep current during the groundschool phase but didn't quite manage it - too busy studying/too tired and I used any spare time to catch up on other things.. I think I only flew 3 hours in 9 months which was expensive because every flight required a club check with an Instructor - and I wanted P1 time, not Pu/t time.
Bear in mind that the exams are time-limited. You have 36 months after the exams in which to do the MEP/CPL/IR and in your case, build quite a few hours.
I don't think there's any harm in not flying, but if you do, it'll chip away at some of the hours.