I can change the times, how long it takes for a tree grows

In your game directory, you find a file called "commons.jar" in the "data" subfolder. You can open this file with a zip program (WinRAR for example), then navigate to "commons/definitions". There you find a file called "definitions.db", this file can be extract and opened with an SQL editor (like Navicat). You find a table "Plants" in this database file, which contains a column "growTime" for each plant (realtime seconds until the next growth stage is reached), you can change that value. Once your done, you have to move the .db file back to the .jar file
PS: If you want to change it for multiplayer, too, you have to edit the commons.jar file in the server lib folder accordingly