Takes a full day to prep, paint, and overnight to dry. Especially if you screw up the tape job and have to respray everything again.
As far as prep work, just wash it down to remove any dirt. Grease remover is a good idea if you have any lying around. I was told to sand down the plastic lightly but I never did and it turned out fine. I tried taping off the lettering I wanted in a different colour, but ended up stripping the paint cuz I took it off too early. Not to mention cutting the paint with the blade I used. Hand paint the lettering if you're going to do that. I had to smudge the paint a bit to get it looking decent as it came up very 'watery' at first.
http://members.optusnet.com.au/spyper666/car/DSC00595.JPG
One thing I can't stress enough. Do NOT put the cover back on until it is fully dry. Even if it takes two days, let it dry properly. I put mine back on too quickly and the engine heat made it bubble slightly in places. Still doesn't look too bad though.