Generally speaking, whenever I feel like it. I guess it tends to be more often on weekdays because I work at home, and I'm alone when I work, so I can and will masturbate regularly in between. Also, often it's the first thing in the morning. More often than masturbating before going to *****. I don't always look at porn, I often use my imagination (although it's not uncommon to fantasize about pornstars).
Aside from using my hands, I also like to use a vibrator sometimes. If you've never tried it as a guy, you really should. Just try holding a vibrator against the tip of your cock and enjoy. When I tried that the first time, I came before I knew what hit me. But that was the max setting.
It's also nice to strap a vibrator to your cock with rubber rings, set it to a low setting, and just lie back and wait for the vibrator to work its magic.