Gunpowder can be used as a timed fuse for TNT.

If you want to prank your friend but want to time it to a time that you aren't online you can place down a couple lines of gunpowder and it will be perfectly timed.

Or you could craft a fuse using gunpowder and string and just place it like a lever but when you right click on the placed fuse it will open a GUI where you can set time, say 15 minutes, and 15 minutes from when you click confirm it will ignite the TNT.