Traveler: Basically you become as powerful as a Godlike, so basically you become as strong as Collector
You can it use whenever, but you must have a bit of energy, if you don't have any energy you can't use the technique.
Once you use the technique, you get all your energy back (100%) and more (300%).
But once you get to 0 energy again, you'll go back to base form with all your stats put to 1.