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**.