This would be a good question to ask Castle, because it's going to vary from manufacturer to manufacturer.
I can give you some generalities, but I'm not a user of ESCs -- I'm a circuit designer who has designed brushless controllers similar to ESCs. I could probably design an ESC (at least one that'll turn a motor -- maybe not one that's worth spit). For going out and having fun, I fly slime (this is because after you add the sound system and the smoke generator, electrics are way heavier than slime). So I have to make some assumptions which may or may not be correct.
So, here's what I know:
"Gain" probably means the proportional gain in a speed-control loop. As you increase gain your current draw will most likely increase, and your motor's response will get snappier up to a point. Beyond that point, your current draw will increase but all the energy will go into making noise. So you can save on current draw by decreasing gain -- but at the expense of response coming out of corners. This same rule applies to KR timers, too, because Keith does the same thing with his timer that a helicopter ESC does internally.
"Timing" refers to the way that a sensorless brushless motor controller works. Ideally the ESC will control the motor's terminal voltage so that the voltage that's going toward turning the motor is in perfect phase with the switching of the magnetic field across the stator. Unfortunately, motors possess a characteristic called "leakage inductance" which effectively slows down how rapidly the motor's coils respond to changing voltage. The "timing" parameter is, as far as I know, a way of compensating for this -- the ESC knows where the motor position is from monitoring the voltage on the terminals, and it uses this knowledge to switch the voltages around a bit earlier than the motor "says" it should.
I don't know what the heck the "PWH" parameter is that you're talking about, so I won't comment on it.