Tip: How to stop minecraft from pausing when you alt-tab in single player

If you right click on a furnace (may work for crafting tables and chests as well), then minimize, the game will keep ticking without pausing. This is useful if you want to wait out your first night, let some ores smelt, wait at a mob grinder, etc. in singleplayer without waiting.

This may be common knowledge but just discovered it, may be of some use.