It's probably different for the smaller bars. I've never had a saw with less than a 28" bar. I always on the older J'reds, back the screw out until I feel it's jumped off the thread and then back in maybe half a turn. The idea is if you're using a saw all day, you run out of oil & gas at about the same time....unless you have the addition of a manual oiler as well. If you're trying to save money on bar oil and you're gonna let it run out of oil before it runs out on gas, you'll just cake the cutters with hardened pitch. In fact, that's a good way to tell if you're running out of oil...look at the top of your cutters.
Kevin
Kevin