I read in the past that training is not linear so with the OP's question maybe I am inclined that 48+ is still optimal versus 48. It is not a big deal in the sense that you would want to give your second trainee his shot at 48 minutes as well instead of choosing your primary trainee to bump from 47 or 48 mins to 48+. If I have three trainees, BTW I never had because it really is unrealistic to have three if you do 1 position training most of the time. The question for the OP is how may trainees do you have? If you answer 2 then get the 48+ if more leave it as at is.