Good morning Buddha,
Well, althought there may be others with better procedures, for me, it's a matter of doing one color at a time, then allowing it to dry/cure completely before starting the next color application. There is no way to short cut the benifits of waiting until the previous coat of paint is completely cured... yes, it's time consuming, but the results will speak for itself..... (not to mention the mental trauma that will be avoided by NOT peeling up a section of the previous application when you're removing the mask)
If however, there's a "fuzzy" transition between the colors, I definately would apply each color on the same day using an airbrush, either freehand or with paper patterns held just above the model surface.
The bottom line, when working a two, or three, or four tone finish, letting the previous color dry completely is the best bet.
Take care,
Frank