It' varies, it depends on food intake, animal's age etc, they can go without a bowel movement for WEEKS.
Now the fact that you are underfeeding your BP is the main reason why there is no bowel movement as most of the prey is utilize for growth leaving little to nothing to be eliminated.
Hoppers are what people feed BP out of the egg and they quickly move them to adult mice, if you have had your BP for 2 months and still feed hoppers there is obviously an issue here.