You probably only need one coat. But if you want another coat, this is from the instructions: "If the second coat is applied too late it will not adhere because of the slick surface and will peel."
Tomorrow you can use TIE-COAT PRIMER or ETCHING PRIMER that they sell at POR15, or sand/scuff as jonmc56 mentions. Then put another coat of POR15 if you really want it, or just put a primer and/or topcoat on of your favorite paint. I have had success with misting the POR15 with Rust-oleum spray can primer while the POR15 is still tacky, and then you don't have to do anything special.
I think for a frame, if it were mine, I would consider it 100% done if you leave it tonight and not do anything more with it.
http://por15bc.com/por-15.htm