In general, I recommend 45-75 minutes per weight-lifting workout, 4-5 days per week. Especially in the offseason when lifting heavy and intensely, this is all the time you need to stress your muscles and CNS. Spend the rest of your time eating, sleeping, and resting well in order to recover and grow muscle.
During contest prep, you will likely be doing cardio which will be additional time in the gym. This is okay.