I checked MCreator, go to the AI and Goals tab and choose from AI templates: mob that only attacks when hurt - it works like a zombie pigmen - he is fine until you hit him.
Next step is going to spawning. You want day right? I guess creature is fine. It spawns in day time, yet on grass blocks


Other is the procedure spawning:
If - is day in the provided world
do - spawn entity (name) at x x y y z z etc.

I just guess by logic now, what I have here, yet if you will have issues with the procedures, then I could try to help(workspace share)