I've only needed one twice
The first time....I'm not sure....it was after I had overdosed. But generally I think between exes mum ringing them and them arriving it was only about 20 mins (though this was circa 2009)-that does sound stupidly quick granted, although I should probably add that not that long after being admitted I did almost die and have to be resuscitated.
The second time I'd called 111, had all the symptoms of a stroke so had no choice but to be blue lighted to hospital though thankfully it turned out to be Bells Palsy, again that was very very quick.
I've fortunately never been in the position of having to wait hours.