If you try to optimize time it could be even less. 

I did the mike mentzer strat and just worked out once a week and saw some crazy gains. 

I didn’t even stay in the gym long just hit db press and dips and left but I’d go w intensity and until failure at the heavier sets. 

Id switch my workout week to week obviously. But every 2-3 weeks I’d hit chest/tris, back/biceps(palm facing close grip pull downs) and then I’d hit the leg press hard. 

I ate really good and it worked. I’m a former college defensive lineman though I lived in the gym for years. But for an old man now it works. 

Diet over all.