From the time I pick the weight to do my first set, to the time I complete my last rep for my last set of my last exercise......about 45 minutes = 3 hours a week. If you are pressed for time, your form is good, your intensity high and your diet right, this will work just fine.
Serge Nubret, for example, lifts weights 4 hours a day, I believe every day of the week. That has worked great for him and he was a pro, but there is no way that I can spend that much time in the gym with my job and other commitments.