Most people find dry fire incredibly boring – me included. I think it’s a mistake to set a time limit (i.e. dry fire for 20 minutes) because this kind of tedium winds up with you watching the clock.
I recommend giving yourself a set number and break it into small bites. I try to dry fire 200 times each day, broken into bites of 25. I like to start with 25 strong hand supported, 25 weak hand supported, 25 strong hand only, then 25 weak hand only. I usually stand very close to a bare wall for these, and allow myself to consciously reset the trigger.
For the next 100 I like to practice dry one-shot draws… if I’m feeling frisky I’ll incorporate weak hand draws. Generally I pick out an aim point for this series instead of the bare wall. Dry fire is great because it don’t cost nuthin’ and you can focus on perfect presentation and trigger press, allowing you to work on increasing your speed with live fire at the range.
Don’t be afraid to use your .38 snubbie (especially CT laser equipped!) for dry fire! The heavier trigger and visual feedback from the laser will translate positively to your service pistol. Not having to reset the trigger with the slide makes it go faster as well! I don’t particularly recommend dry-firing your carbine… you’ll get more benefit out of sticking with your handguns. Believe me, the trigger manipulation *will* translate over.
The above is not "The Law as Told By Jay"; it is simply an expression of some opinions that I've formed through my training and experience with several very good instructors. Please feel free to discuss and disagree!