In case you didn't know, O-Power energy is the orbs at the bottom of the menu for O-Powers that get used up when you activate an O-Power.
It takes 4 minutes for an entire circle to regenerate. So, if you were to use up all your orbs it'll take 40 minutes for your entire orb bar to completely regenerate.
Source: http://bulbapedia.bulbagarden.net/wiki/O-Power
Hope I've Helped!