Once you have performed the action you reap the reward. Instantaneously.
For instance, once you drink a subject's blood, your blood pool increases by that amount as you do so. There is no delay. Also, in the case of healing, once so many mintues have passed, you may erase that level of bashing damage you've taken.
Once you've done something monstrous (truly monstrous, not just scaring the neighbohood children with a mask, but actually tormenting them, giving them an emotional trauma that they carry with them) you gain the willpower.
It is very difficult to gain an additional point of willpower by doing the same thing a second time in a row in the exact same fashion. Usually it requires a change of scene or subject. (You cant drain a husk, for instance. It's gotta have some juice left! You can't give care to the guy with the leg you already fixed, it's fixed! Psychoanalyzing him so he doesn't have night terrors is acceptable, however.)
source: personal experience, Werewolf, Mage, Orpheus, which used nature/demeanor.
Disclaimer: White wolf is not known for "Crunchy" rules that have a strict codification. As such, many take liberties with such hazy ideas as regaining a mechanical advantage when roleplaying a particular event or type of event. These have been the rules that I was taught and consistently the ones that were reinforced. Once I get home and actually go back through my copy of Vamp', I will be able to quote the willpower passage for you.