A PhD can be very time consuming when compared to undergraduate life. For a start there are a lot less holidays (eg 8 weeks, incl public holidays, for BBSRC funded students). However these holidays are better than most full time jobs. Hours may sometimes be longer than full time employment but will probably be more flexible. Don't expect to be able to take regular half days for sports fixtures. Most students are much busier in the final stages of their PhD, but most manage to maintain an active social life over the course of the PhD.