Make sure your nipples aren't aroused when getting it done. Being cold/excited will obviously make it much more painful.
As a person with breasts I experienced pain in the entire "boob" area for about two weeks, and when it was cold I felt that same sensation for about 6 months. My friend who doesn't have breasts got his done at the same time (we made it a bestie date when I turned 18). He didn't have nearly as much pain for nearly as long as I did.
Being cold sucks while you're healing. So if you get this done any time soon and you live in the northern hemisphere, prepare to layer up and keep them nips from stiffening. Cuz it HURTS!!