Painting camouflage which color first

Lightest first.

I bought a sheet of clear acrylic at Home depot and a few hinges. I cut it to size and mounted that to my spray booth. When I am waiting for something to dry, or taking a break, I leave the model in the spray booth and close the "door" to keep dust away. Holding it tightly shut with a few clothes pins.

I use the "lightest first method",,,,except for one group of Aircraft

for Light Gull Gray over White aircraft, I use the Light Gull Gray as my overall base coat, it helps the white cover the plastic color better

I also use the smell method,,,,,I put my freshly painted models in a plastic storage container with a snap on lid,,,,,to keep the dust out,,,,,,I pop the lid once in a while to give it a sniff,,,,,sometimes, I have to take the "bottom" off and smell the model,,,,,,the softer plastic will sometimes pick up the odor and hold it

also,,,,,use the lid as your base, the bottom as the cover

Rex

I usually wait 24 hrs at a minimum - however that can change if the humidity in your area is higher.  An old  trick I learned years ago from an old model railroader is to sniff the painted are - if you still smell paint fumes, the paint hasn't cured yet and shouldn't be painted until the smell is gone.

I use Tamiya acrylics and spray the base color, dry the model in a drying booth for an hour and do the next color.

I wait 3 days or more, just to be sure.  Especially if I'm masking.  If free-hand and in a hurry I may only way a day.  One trick I use is to paint the entire model the underside color (if it's the lightest) and use it as my primer coat to check for flaws. 

Lighter colours first generally to avoid having darker colours show through the lighter one. Dry time can change from brand to brand but I usually wait a day between colours, a little more if it happens to be very humid.

Typically you start with the lightest colors first.  And with enamels you should probably wait at least 24 hours between layers.