If you want to get anal, it actually depends on what lifters you're using. Comp Cams advises 1/2 turn to 3/4 turn depending on what lifter of theirs that you're using. You can probably look on the manufacturer's website and they should tell you what they recommend in either number of turns or in a dimension of preload.
For instance, if they tell you that .020-.040" preload is good, then you can judge how much .020-.040" is by looking at the threads on your adjuster screw or measuring how far the plunger is depressed in the lifter.
You should be safe with 1/2 turn though.
