The way I've always done it (25 years or so)...
I have a home made thing to hold the case being annealed in the drill (made from a socket), I never gave drill speed any thought...and I use one torch.
In a room with very dim light, turn on the drill and hold the case to the fire until "the instant" you see it begin to glow (turn red)...then dump it in water.
The dark room is necessary...otherwise, by the time you see it turning red...its too late, the case will be too soft. Brass doesn't harden when it hits the water...water only cools it. The only way to harden brass is to "work harden" it...and that is kinda hard to do if its buttery soft.
It takes just a little practice to get the rhythm down...but before you know it you'll have 100 or so cases ready.