The max return on a dropped ally is 60% which is 15 days after you bought them. It doesn't increase any more than that.
Charizard, you are incorrect, and you should not answer a question if you are uncertain. You're just perpetuating the misinformation and idle chatter that plague the forums. This hasn't been the first time you've been called out on it. I really hope you get your imminent forum ban soon.