Weeks?? Oh good heavens no!
MONTHS!!!
seriously, most paintjobs will dry to the basic touch in one day. meaning, you can touch it, but don't press into it. The outter skin will be dry, but the paint under the surface will remain soft for acouple days. (depending on the heat & humidity). If it gets cold at night, (and depending on the color), it can blush over, and get a milky look to it.
so, just pick your paint days wisely. Check the forecast. if it looks like rain or cold, try again some other time. And since you're painting such a huge rig, have EVERYTHING ready the night before, all prep work done, and get an early start when you do go for it! (hey, if you finish early, then this'll give the paint time to dry before evening, and you can sit back and enjoy your work!
As for diluting your paint...yes, it'll take acouple coats to get the coverage you want. (you're painting with thinner paint). but since your applying a thinner layer of paint on the bus, the outter layer drys faster, thereby allowing the inner layer of paint to evaporate and dry faster too. Acetone helps the evaporation process along.
One thing, is the primer layer is very important. Did you say you're painting the bus white?? If so, then you must have a good solid neutral base color, otherwise the colors underneith will show through. A good gray primer will neutralise any colors you're trying to hide. (white does not hide anything!) This is why alot of folks do repaints with strong or darker colors...they hide old paintjobs much better.
Sorry brother....you'd might as well paint a battleship with this news!!