How long does it take to replace a Rear Quarter Panel? DIY?

You better be a darned good welder and have a lot of experience with thin metals. too much heat or applied too long and you'll have warpage that isn't pretty. This is not a job for an amateur unless you don't mind it looking like crap. I'm not a body man but do some small stuff. Definitely wouldn't get into welding replacement panels without plenty of experience.