All the literature I've read for bodybuilding says your reps should be in the 8 to 12 range, and higher reps leads to more muscle endurance without much muscle growth.
Yes, 4 sets of 8 to 12 reps. Takes, say, 1.5min to do the reps. 1 minute of pause in between. Four exercises per muscle group. Two muscle groups per training session.
So you're looking at (4x1.5+4x1)x4x2 = 80 minutes == 1 hour 20 minutes minimum. Without counting the time to move from one exercise to another, without changing your clothes, without falling into a conversation with a fellow gym member, without waiting for anyone to free up a machine/weight-set/whatever.
Face it, if you're bodybuilding you're spending 2 hours a day at the gym.
Just getting strong or fit can be done in much less time, though it may leave you without the beach muscles, if that's what you're after.