Glued on patches should last as long as the tubes and I've ridden them for over a year until some other failure trashes them. My punctured tubes also go in the pile until I have enough of them to bother with patching and can use most of the cement. But that can take years.

A few weeks ago I got double pinch flats. I replaced the rear tube and patched the front with a Park "glueless" patch in 45F temp. I'm going to leave it on to see how long it lasts.