I very, very rarely use social networks. I probably log into Facebook once every couple months, but usually just to look at their UI instead of actually looking at the content. 😛 The social network I use the most is Twitter, which I check maybe once a month. I use forums more than anything else.
God, I spend way too much time on social networks. I check Facebook probably every twenty minutes or more. Mainly because my phone get's blown up with notifications. Twitter is a rarity, though. And, I use Instagram so I check that often too.
Honestly... not that much. Maybe 30 minutes at the most. Some days I don't even check FB at all. I don't make it that important in my life so it doesn't run my life.
I invest at least 30 minutes a day on social media, usually in 5-minute bursts where I'm either responding, scheduling, wishing folks a happy birthday, or trying to create engagement.