How long should you train?

Like almost everything else related to bodybuilding, I am finding conflicting advice/instructions about workouts, particularly regarding how long you should train in one session. I read that 45mins is a maximum though often I read about people doing 3 hour workouts. Personally I find that to do 4 days per week I need to work out for about 2 hours to cover all my body parts.

i.e.
Monday
Chest, shoulders, triceps.
Tuesday
Back, biceps, legs/calves
Wednesday
Rest
Thursday/Friday repeat
Sat/Sun off.
(On rest days I do cardio, have a coffee, enjoy life.)

I aim at 4 exercises per body part, (i.e. chest: barbel bench press, cable flys set up high for lower chest, incline db press for upper chest, pec flys) 4 sets at 6-12 reps. 30 second rest between sets, sometimes stretching out to 1-1.5 mins to get my breath if it is a particularly aerobic exercise. Some of the sets I do are drop sets or supersets (i.e. db front raises, side raises, rear delt flys. No rest between, 1 min rest between sets) so that takes a bit of time.

I have been working out for about 10 months now, 4 days per week, and it is fairly consitant 1 hr 45 min to 2 hours to cover everything, including of course setting up weights, putting weights away, water bottle fills, bladder emptying, etc. I try to stay focused, keeping any conversation to rest times or setup times. Bit hard when they are an attractive doe eyed chickybabe.

I have started to take a protein shake 2/3 of the way into each session as I don't want any catabolic stuff happening.

Any suggestions? I have heaps more to ask but will start with this one. Prepare to have your brains picked.

if you can fit your workout into 1hr its good. If you cant, i dont think its that bad. Although 3 hrs seems to be over doing it. Its a long time without eating and it probably means your wasting a lot of time. I tend to get mine done it 1.5hrs