Speed reholstering, bad idea. Say Uncle links to an article talking about the problems inherent in holstering a pistol. The worst part is that you're liable to shoot yourself, which is bad juju at best.
Draw your pistol with the speed necessary, of course. As Wyatt Earp so famously said, “Fast is fine but accuracy is final. You must learn to be slow in a hurry.” Once you've taken the pistol out, there's no reason to be in a hurry to put it back. Take your time.
"But, PawPaw," you ask, "how do I present myself as non-threatening if I don't immediately intend to shoot?" Simple, my child. SUL position. It's explained here, but a picture is worth a thousand words.
Once you draw the pistol, everyone is going to know that you're carrying. There's no rush to put it back in your holster, indeed, it shouldn't be holstered until whatever prompted you to draw in the first place has ceased to be a threat. You can re-holster at leisure. Safely, with your finger off the trigger. Learn to use SUL. It's a great gun-handling skill.