There's a lot of variables with my training that will take up time. When i'm training specifically for strength,I am in the gym 2 hours. Training for strength is a tedious process of loading and unloading weights(a lot of time more then you can lift,but isolating certain parts of the exercise,ie. board presses,rack pulls). You can't just wait a few minutes in between sets,when you are going balls deep in it. You will be weaker.Strength training is best done in groups of people that have similar goals. It's flat out dangerous imo,but there's nothing like it in the same regard.
When i'm doing a bodybuilding regimen,I still love the upper/lower split,but most of the time that's just not reasonable,because i'm doing 3-4 exercises per bodypart.
I always group at least back and legs together,because I can deadlift and squat on the same day without it deducting from recovery and straight up just being sore. It's a real pain in the ass if you squatted on monday and you're trying to pull on thursday. Most of the time i'm really feeling the squat soreness by day 2 of recovery.
I'll usually split mine up something like this.
Chest/tri's/bi's
Legs/back/abs
Chest/shoulders and any auxillary work I haven't done. (grip training,sledge hammering tires) I train chest 2x a week,because it has always yielded great results for me. If my chest is still tender I won't train it,and i'll do something else. I'm a big believer in the "listen to your body" thing. On paper it doesn't really look like that much training,but in the gym it's a whole different story. I put a ton of time in compound lifts and use the isolation lifts to really get a good solid feeling going. I also do cardio 4x a week. On average when I'm doing bodybuilding splits I'm in the gym about an hour and half.
Don't leave the gym til you are satisfied. Unless you have something else you gotta be doing there's no reason to fall in love with the clock or let it mess with your head. Your body or a piece of paper doesn't know that 3 sets was enough. You do or don't though. That instinct gets stronger with time and experience.