It took a while for Leon to understand how Foresight worked. Basically, the time in his head passed two times faster in comparison to the time outside his head while the skill was active. For example, by keeping the skill activated for two seconds, Leon would be able to see the things that would happen two seconds later... It wasn't an overpowered skill as Leon had imagined, but as long as he keeps recovering his mana and also his practice the skill, he would be able to overcome even the cooldown time.
"I can't use other skills while I use Foresight... so the best way to train the skill is by using the mana on my Soul Eaters," Leon concluded. "The problem is, while I can see the future, the future might change according to my actions. So, it isn't a good idea to rely on Foresight during a battle."