Is there a reason why several sources on pumping mention that the
maximum time at each session using any type of pump should be no more
than 30 min? Is to ensure the mom doesn't develop over active letdown?
Or is it because or some other reason I don't know?

I'm one of those who has never seen an OAL. I experienced engorgement
but not where I had pain/plugged ducts or such stuff. I have letdowns
few minutes into nursing/pumping. So does this 30 min limit apply for
moms like me too?

Thanks.