I am a complete noob to the game, but I try to dry fire anywhere from 10 minutes to an hour at a time 3-4 times per week. Mostly just depends on how much my wife can stand to listen to that particular night...
I also do some dry fire in between live fire strings at the range, mainly to work on trigger control. If I feel I'm starting to get sloppy on the trigger and/or anticipate recoil, I'll stop and dry fire for 5-10 minutes to settle myself down. Since I started doing that, I notice that I can shoot more and more live fire without needing to dry fire to refocus myself. My goal is that when doing practice live fire I don't "program" any bad habits. If something gets out of line, I stop and address it.