I would say three to four times depending how fights plan out but could easily be two if cuts come in to play for the big name boxers should be looking at three at the very most.
3-4, barring injuries and cancellations. Problem is guys thinking they only need 2 fights per year and then getting injured/opponent withdrawals, etc. Plan for a full year and scale back as needed. Guys on the way up (4-8 rounders) should be fighting 8-12 times per year, especially if they're stopping guys early. Not like they need time to build up their fights, nobody even knows their opponents. No way our Olympians should still be getting the soft treatment for this long and only have 12 fights. Hurts them in the long run.
1 to 2 times, preferably 2, for big name fighters like Pacquiao and Mayweather. Guys slightly below them should fight 3 to 4 times. Low level guys can bang about 6 times.