strokes everyone takes

For 18 holes, four hours is the estimate by most people .
The actual time depends on how busy the course is, how many strokes everyone takes 
(a round of 72 will obviously be faster than a round of 112) and how many people you
are playing with. A foursome playing a very crowded course might wind up spending 5
or even 6 hours on the golf cours.
For suggestions on ready golf and keeping play moving.A golfer playing alone on a
course that is not crowded should can  finish in 2 and a half hours or less.
To keep things moving, all friendly matches (rounds of golf that are not played in
tournaments or for money) should be played by the principles of "ready golf."