CLR cleaning before paint

[Midgets50]

so in a few weeks im going to have my truck clear coated and am going to use CLR to clean it to keep that original patina look. My question is how long do you guys scrub with the CLR. i left the brake cylinder i though i was going to use in it overnight because i forgot about it. Came back and took it out and it looked like new. i know i cant do this to the truck but just wondering how long you guys would sit and scrub and what methods you guys would think would yield the best results. id post a picture so you guys could see the patina, but for some reason it wont let me no matter what i do with the picture