I used to play Pixelmon a few years ago and my friend set up the server. When he did, he made it so that every 5 minutes any Pokémon that had spawned would be cleared. This was to allow for new spawns, which is especially helpful when hunting rare or shiny Pokémon. It was set up in a way so that shinies and boss Pokémon don't get wiped. I have gotten the 'Spawning' file in my Pixelmon folder but I can't find anything in there on how to set this kind of thing up, and Google has nothing either.
Any help would be greatly appreciated, thank you :)