Miss D;
There is an ole saying, "you can never miss fast enough"....
I think your question is not how long it takes to get out of the holster until firing, but how long do you take to align your sights and then press off the shot?
From the low ready position, after breathing control and exhail of the final breath, starting to raise the handgun onto target, should be about 2-5 seconds before the shot is released. That might mean you are on target concentraing on hold control and sight control for 1-4 seconds. It takes 2-3 seconds from exhail to extablish sight perfection and start the trigger control. After about 7-8 seconds, musscle, hold, sight control will suffer. So, general time, for extreme accuracy would be 2-5 seconds. You could also apply this to rifle shooting as well.
For defensive shooting, you will obviously not have the luxury of taking your time for extreme accuracy. At a standing fighting position my sights are on target before they are aligned with my eyes, so dependent on the distance, the shot may be released early.
From relaxed arms, holstered, standing, until the gun fires, the time could be as short as .80 second from the retention position at CQB distances of 10 feet. This would mean that the time from sights aligned on target until the trigger is pressed could be as short as .15 seconds.
Aimed head shots from the same hostered starting position at three yards are reasonable within 1.5 seconds. That is about 1.0 second to draw, about .30 second to establish a flash sight picture and .20 seconds for the trigger press (trigger preload is performed during the flash sight picture segment). And, the head shot could be center mass, I just use head shot as a reference of the accuracy skill level which should be expected.
As stated by previous replies, each different shooting decilpline will require different speeds. Regardless of the type of shooting you are performing, of course, when you first start, we take the time required to learn the skill in a slower motion. If extreme speed is the requirement, it must not be gained at the expense of acceptable accuracy.
Best Regards.....
"Train to Defend, Train to Survive, Train to Win"