[nsilvestri]

>they also have jobs

bold assumption ;) other options include being retired or having a partner provide for them

>how many hours people spend

I'm not one of them, but I'd probably guess it's anywhere from 2-6 hours a day. Depending on job, one could easily can work that in before/during/after work. /u/GallowBoob, the user with the most karma on reddit, actually managed to turn it into his job. He was originally a landscape architect whose reddit habits got him a job at those awful viral licensing companies, although now he does social media directing at an eSports company.