The only time I dunk em is to find the leak(s), which usually is not necessary. If the leak is not readily found (in which case I usually cannot inflate it much), then I over inflate the tube quite a bit, and rotate the tube by my cheek. Once I find the leak then I buff the puncture area and spread the cement widely while inflated (it will be quite smaller when deflated). And in so doing I spread some cement over the puncture hole so that it makes a small "geyser," which leaves a white spot so I can see the puncture. The cement also dries quicker due to the over inflation, and when dry then I deflate it and press the patch on well, with the white spot I made being in the middle.

Some people let it sit for about 30 min, but I usually inflate it somewhat immediately (due to people waiting) to make sure the patch holds and check for other leaks. And sometimes there are more leaks, and in the case of curb hits there are almost always 2 on near opposite sides. If the patch holds then then it will almost always hold when inflated in the tire, and never leak.

Note however, that as described in this thread, I am coming across more tubes which have a distinctly different and slippery feel, as they seem to be coated with some sort of plastic, and the cement will roll off such (in pieces) after it has dried. I find have to do the procedure twice for a patch to stick. Perhaps some tube makers are trying to sell more tubes. Maybe REMA would work better.