I have not quite worked out the best time to remove the masking tape, but I'm leaning toward sooner rather than later. One problem that I have gotten is that if I wait until the paint is in the "gummy" stage, when I pull up the tape, it leaves little spikes and a raised ridge along the mask line. If the paint is a bit "wetter" when you pull up the tape, that ridge will settle down and level out on its own. Also, some paints go through a phase during the cure when they actually lose a bit of their bond with the base layer (or at least they seem to, anyway) before reestablishing it later on in the cure process. If you try to pull up the tape then, you run the risk of pulling up chunks of the new paint that is still curing. But if you wait until the paint is fully dry, you will often have this distinct lip at the mask line. Even if it isn't all that visible, you will be able to feel it with the tip of your finger.
I suspect that the ultimate answer is to apply your second color in a very light coat, adding just enough to get an even, opaque coat, but no more. Doing this solves a whole lot of problems. If there is less paint on top of the masking tape, there will be much less of a chance of getting a bleed under the edge. Bleeds occur because a mass of wet paint sits at the edge of the mask line, and eventually starts to break down the tape's adhesive along the edge and then work its way under the tape. A light coat, on the other hand, will dry before it can start to do that. You don't need to use tape that has as much tack to it if you spray just a light coat of the second color, so pulling off the tape will be less traumatic. In fact, if you look at where your overspray goes in your work area, you will find that you can get effective masking without using an adhesive mask at all. The edge of a sheet of newsprint can leave a clean mask line in your spray area or booth because it doesn't get flooded with paint in the first place. Now, I wouldn't recommend masking off areas of your model by just laying newsprint over them, but this phenomenon does illustrate the fact that you can get an even coat and a clean line without needing to apply heavy duty masking if you just go a bit easier on the paint.
A light coat of the second color will be less likely to run, so it allows you to pull up the masking tape sooner. A light coat of the second color will also leave much less of a lip or ridge at the mask line, if it even leaves any at all. A few coats of primer and paint can add significant weight as well, so going easy on the coats will give you a lighter rocket in the end, too.
Finally, darker colors and metallics cover really well. Since you are masking off light colors in order to apply darker colors or metallics, you can create solid, even and opaque sections on your model with a lot less of the darker colors than you needed to use when you applied the lighter colors (especially white).
The whole issue of masking suddenly becomes much less of a headache if you just remember this one principle. I learned it after making all of the mistakes that I mentioned above. Multiple times.
MarkII
