Can anybody tell the magic how to make hemp (clone) growing slower? e.g. 1-2hours 

You can just open

PlantEntity​

class and see that there are some params that can help you

public class PlantEntity : BaseCombatEntity, IInstanceDataReceiver{... public float realAge; public float growthAge; private float stageAge; private float lightExposure; private int seasons; private int harvests;...}​

If you need exact plugin for that - you can hit me in discord - Orange#0900