Truthfully here, my "rate of deflation" ;) will vary, but typically, I will stay "semi" for a considerable length of time; all the while certainly remaining quite usable at that-- and, often resuming "full mast" for yet another go-round without too much added prompting. Surprisingly, it seems the "second erection" can seem even more monstrous at times--resulting in a real gusher, too!
But, again--not always.

More than likely, as we continue reading each other's posts, we're gonna notice (no doubt) that this indeed WILL vary from man to man.