Minimum is usually three times a day (wake up, after work, bedtime), but I have streaks where 6-7 times a day (and lots of breaks at work) is normal, and some hypersexed weekends where I'm bored and keyed-up and over 10+. By the end of those days, all that's coming out is steam, though.
What's funny is that I could rarely manage more than 2-3 when I was a teenager, but the older I get, the more I gotta do it. I'm gonna be the most annoying guy in the nursing home, at this rate.