The Divine Devil's fruit wasn't as bad as the Spirit Cleansing lily in terms of difficulty on when and how to pick it.
The how part was incredibly simple. You just picked it like any other fruit. There was no specific way on how to pick it, just when.
For a Divine Devil's fruit to be usable, you must pick it when it is between 120 years and 123 years old. Any fruit picked out of that range was useless.
If picked too early, you would end up with something that would actually poison you. That was what had happened to the city lord's mother. If not for him having accidentally made a pill that could help her sweat out the filth in her body, she would've forever been in a coma.
If picked too late, however, while you would still end up with a useless fruit when it came to Mortal Cleansing, you could plant it to grow a new Divine Devil's plant and grow more fruit.
