it's three hours total spent making the game, so three hours from when you start if you are doing it in a single sitting, or you could do an hour and a half one day and then an hour and a half the next day, whatever best fits your schedule I guess
this is according to this post made by the host during the last godot rumble so I'm assuming it still applies: https://itch.io/jam/godot-rumble-2/topic/3107333/theme-for-the-jam#post-8525586