Couple things, I really don't think missions starting every 30 min is often enough. If I crash on take off I am not going to wait around 30 min for the next mission. I'm going to go play something else. Granted that might be the MA, but it might be another game altogether.
As to mission length, I'm sorry, but even at age 40 I don't have the patience to spend 60 min flying to a target in B-17 and then 60 min flying back. I certainly do have the patience though to climb for 10 minutes to intercept the poor claude who just spent 60 min getting there. I suspect that will be a common preference.
Both the above concerns can be addressed somewhat by allowing gunners to join in flight. That way, if I crash on take off I can at least join another mission as gunner while I wait. (Which makes me think that the optimal time to attack a bomber formation is at the mission start times. I bet 80% of the gunners will be leaving. ;-)
I think serious thought should be given to air launching of bombers and making those bombers be drones that a player can join at any time. Get rid of AI gunners altogether and treat the bomber group just like an airfield with mannable guns all around and some sort of broadcast notification that an enemy is approaching.
And by all that is holy, do NOT base the time people are willing to spend on onling "RPGs" I've played 'em and I've played online combat sims. I spend far more time and money on the combat sims that I do with the RPGs because, by and large, the RPGs quickly turn into a pointless level grind. One persons voice, but I really think the audiences and expectations are different.