there aren't really rules that dictate how fast once you start fast regening.
The default zone data is 180, this is 180 seconds to regen to full. If you want it to take 30 seconds, set this to 30. (At least I think that's what it was when I was figuring this out) You probably also want to lower Character:RestRegenRaidTimeToActivate and Character:RestRegenTimeToActivate
Code:
UPDATE zone SET fast_regen_hp = 30, fast_regen_mana = 30, fast_regen_endurance = 30;
Run that SQL, should change them all to 30.