Painting a two tone fender

[AirSpeed]

I posted this in the paint section but it seems there's more action here, I'm going to paint a two toned fender today, it's off an 80's Chevy dually rear. I've painted before but never two toned, the colors are light yellow and white, the yellow being below the first body line and around the wheel opening. Not sure if I should spray the entire fender white then mask off the white and spray the yellow or what! Any tips on masking and what procedure to follow? Also is it best to remove the tape right after spraying or wait till it hardens? I'm using urethane if that makes a difference. Any suggested would be greatly appreciated!