[themightytimmah]

OS first, I've waited as little as 15 minutes between coats of OS, and 45 minutes before topping with a 'nuba, with no ill effects. I think the official word from Optimum is a bit longer though.

You can go both ways with the topping, but 845 over OS is generally preferred. To use OS over 845, its necessary to wash first, or the oily nature of 845 will streak the heck out of OS.

I would think about the look you want before topping - on a black car, 845 improves the look a lot, however on metallic or pearl cars I find that 845 really knocks down the flake pop, while bringing out the color and wetness of the basecoat.