oh it has been a while - but when I was there a bus (not always the one you wanted) did arrive every 30 minutes.
there are 2 - one for MK and AK
one for Epcot and Studios
now this work fine for me. the only problem was if you were at the MK and wanted to come back before AK closed. then it was faster to get take the Disney DD bus - from Epcot (BC), from Studios (BWV), from MK (CR) - this means walking over to these buses (or at the studios or epcot taking the boat) (at mk taking the monorail - if you do this would go to GF)