ideal timing for a 3FE?

[Wile E Coyote]

How much water? And how fast do you introduce it into the intake? Engine cold or hot?

'Enough'
Slow pour. I've also seen a spray bottle set to a coarse spray, if you don't have a vertical throttle body (carb or TBI and such) Avoid stalling the motor quickly.
Hot. It's the sudden cooling that cracks the carbon away from the metal, as I know it.