It varies....I work a full time job which of course makes it difficult. My focus outside of work the last month is being on here commenting and posting. I spend a bit of time in the morning before work and at night. At times, I can hop on during the day and get a post or two up.
That said, I suggest you do what you can with the time you have. 15-20 comments a day can go a long way to enlarging your circle of followers and people you interact with.