I left the ABS cement on for 24 hours. I had wrapped the leaking point with
strips of plastic woven fabric, laying down glue, a glued strip, and then
lots of glue on top to seal.
So far so good.
The leak was in an awkward place in a solar heating collector system. I
believe that by waiting 24 hours, it was as good as it was going to get. 95
degrees F. in the direct sun helped a bit, too. After 30 minutes, I went up
there every thirty minutes and pressed on the fabric to make sure it made a
tight fit as it dried.
We'll see how it holds as the summer goes on.