From EpicDuel Wiki

Power Hours is a new feature introduced to the game with the 1.1.4D release on April 8th, 2011. The basic concept is that between the hours of 10 - 11 AM (EDT) and 10 - 11 PM (EDT) your character earns 2x as many credits and experience (It does not effect Battle Tokens). In addition, if you buy Experience Boosters you will have another 2x experience added to the current 2x experience amount during the power hour. This makes your character earn 4x experience while using Experience Boosters (Buying Experience Boosters during power hour does not effect your credits gained).