I used to play witha group at my old course, we would be the first group off of the day, play 18 holes in about 3ish hours, sometimes less, sometimes a little more. Always as either a 3some or 4some. And this was a course that was about 6300 yards with a fair bit of trouble. Even when we played all the way back 6800 yards, we'd still play in the same time. There really is no reason that a round of golf can not be played in under 4 hours.