I play a course 6000 yards off of the yellow tees, usually takes a 2-ball 3 hours, if in a 3-ball it's around 3 hours 15-30 minutes and a 4 ball is 4 hours.
Medal play see's us no matter what (3 ball or 4 ball) playing 4 hours.
Frankly anything over 4 hours and I would be questioning where the hold up has resulted from, I can recall a round whereby my partner and I were comfortably cruising around the course with no-one around for 3 holes or so, by the time we got to the 3rd we could see a group of 3 women and 1 guy up ahead at the 6th, using past experience we worked out that by about the 9th or 10th we would expect to be catching them (early part of our course is slow in relation to rest of course).
By the time we were at the 6th we could see the 4 ball standing on the burn at the 7th taking photo's of each other, fair enough - they were visitors, unsure of the course layout we would catch up shortly and be let through....
Well that is what would be expected in normal circumstances, we ended up spending 10 mins or so on the tee at a few holes before deciding enough was enough and cutting across in front of them (I should add that there is a little loop to my course around the turn containing 3 holes), wouldn't usually bother about only getting in 14 or so holes however it was one of those occassions where you are playing well and would be keen in keeping a score