Others have covered it pretty good, but using the Google box on my website at www.n56ml.com turns up four places where I show and discuss the use of peel ply. For example http://home.hiwaay.net/~langford/nacaducts/ , where I recommend you peel it off after about 12 hours (that depends on the curing temperature...it might be sooner or later), but you want to peel it off before the epoxy is fully cured to make it significantly easier than waiting for a full cure, especially if you are using Dacron from the fabric store or something like that. "Real" peel ply is supposedly treated with a release agent that makes it easier to peel off.
There's also a healthy mention of peel ply at http://home.hiwaay.net/~langford/owings.html . Mark Langford N56ML "at" hiwaay.net website at http://www.N56ML.com
