When I say 30-40 mins is normal, I don't mean that everything else is abnormal. You might have brown hair, I might have blond hair, our partners may be bald and our children may be ginger...we are all normal
The sign of effective feeding has nothing to do with the clock.
If babies are happy, and thriving, and their mothers are feeding comfrtably, then there is notning wrong.
Glad you are not worried - you are very sensible!
I think you are at one end of the spectrum, and you probably have loads of milk and a large storage capacity (not the same as having large breasts BTW). Couple that with a baby who is not especially needy for cuddles or sucking, and you end up 'speed feeding'