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Power Hour has long since been removed from the game.
Right now you have:
Guaranteed Gain: Basically the REVERSE of RoT in that instead of shunting your skill gain for a set amount of time like RoT, if you do NOT gain any in a given skill within the given time frame, the game "forces" a gain on a use of said skill that would have a chance for a gain.
Alacrity Scrolls: Current an "OOC" (Out Of Circulation) event item that gave a certain amount of time as a "Power Hour" but only applied to the skill listed on the scroll for the amount of time on the scroll.