Hehe, if you're using over a minute on getting the baron killed, you're definitely doing something wrong.
Have everybody stand in a relatively tight group, and take turns on using holy water. No use wasting mana on aoe when you have aoe bottled up, freely available outside.
Did a few runs a few days ago (to get my last abomination stitchings for Cap of the scarlet savant), and I think we used 30 seconds on downing the baron. Skeletons spawned two times. Imp was used, build is 7/21/23.