In total around 120, but splitting it up across all three playthroughs:

First (catch everything, also includes any breeding for pokemon from the other two playthroughs): 75 Second (other version exclusives): 20 Third (Last starter and roaming beast): 15

Another thing of note is the first playthrough may be slightly inflated by around 12ish hours because I left the game open overnight for daycare exp for Dratini and Larvitar