I am taking my truck apart one piece at a time and removing the old paint.This sometimes means that a piece will sit up for an extended period of time after I apply the etch primer. How long can the piece sit before it has to be scuffed and the urethane primer added. Or does it ever need to be scuffed?

2nd question. Do I need to cut the parts in with final color or can I reassimble with primer only.