Here's how a 3 man team can be effective and it takes just 1.5 hours at most.
1st man in Lancaster's or B17's sets off alone for the city. He needs a minimum of 3 passes to get the city below 50%. Until then 100% supplies are leaving the city to the zones factories.
2ND man sets of in Lancaster's or 17's as the first man approaches 1st drop. 2ND mans target is the ammo or troop training factory. Again 3 passes are required to get it below 50%. Until then 100% supplies are leaving the factory to individual fields.
3rd man sets of after second man makes his 1st drop in 17's or b26's or ju88's. 3rd mans target is the appropriate strat on the front line fields. Pointless bombing individual fields until the automated supply line is effectively damaged.
Ammo strat IMO being the most cost effective target where time and bomber load out is concerned. Of cause if you have a whole bomber squad at hand more strat or more fields can be porked. Your time...your call but it does work.