depends upon how many people get on and off at each place. if they have to stop longer because of wheelchairs. (they can't get off until the ramp is down - which the CM don't do until everyone else is gone)
sometimes the train can't pull into the station.
I would say 25 minutes - could be 45 minutes.
if you are traveling with someone who just wants to ride the monrail - well be prepared to spend hours. there are 3 monrails and some people want to ride them all - doesn't matter that later in the week they can ride the Epcot monrail to Epcot - no they must ride them NOW......