Exp to evolve:
Bronzor (at lv 33): 35,937-8,000 = 27,937
Cranidos (at lv 30): 37,800-21,012 = 16,788
Meditite (at lv 37): 50,653-15,625 = 35,028
Drifloon (at lv 28): 18,439-3,832 = 14,607
Total exp needed to evolve all four: 94,360 exp
Total battles needed at 100 exp per battle: 944 battles
If every battle takes 1 minute, then that’s 15.73 hours. To account for Pokécenter runs and any other inefficiencies, an extra 1.3x should probably be multiplied on for a (probably) more accurate estimate of 20.45 hours.