Early and late fighters
 

Can anybody tell me what's the difference between "early" and "late" fighters when spawning aircrafts in FMB?

Are you referring to the RAF Squadron types?
If so what it really breaks down to is early has 2 sections of upto 6 AC in each. Late has 3 sections of upto 4 AC and can use finger 4 and diamond formations, which are not available to early squadrons.
All formations apply to whole Squadron.

Can't say if there's any difference in AI behaviour between the 2 (I haven't noticed anything obvious.)

I think that is about this:

http://i41.tinypic.com/imtor7.jpg

I am too missing how this work, I select Early for "Spawn area" and then go to "Aircraft" and delete all, save, exit and open the mission again the tab "Aircraft" show all available again...

Sokol1