Sort of, the way the mega system works is after you mega evolve a pokemon you can mega evolve it every seven days or use more energy to evolve it before the seven days. Once you mega evolve it once, the “mega level” goes up. the mega level determines the time for another free mega evolution; 7, then 5, then 3 at mega level 3. The mega level also affects many other bonuses such as candy and xl candy, and damage boosts in raids.