i've had a lot of clients come to me unhappy with their results so i have lessened their workout times and they've improved quickly
there is no reason for a weight trainer to lift a long time. these guys who claim they workout for 3 hours are full of shit. they probably spend most of the time talking to girls or playing with their phone. i once watched a couple dudes have a 30 minute conversation right in the middle of the gym lol.. i did my entire workout while they blabbed
I usuually keep my weight training under an hour. Some days like legs I will go over some. I train with intensity so I typically dont have anything left after 60 minutes.
30-40 minutes is pretty short man. Even if you are a high intensity trainer, I don't see how you can properly train a muscle group in under 45 minutes.