There is a very specific golf rule which deals with a very specific situation; when your golf ball is overhanging the hole.
How much time are you allowed to wait to see if it falls in?
Rule 16-2, deals with this:
Ball Overhanging Hole
When any part of the ball overhangs the lip of the hole, the player is allowed enough time to reach the hole without unreasonable delay and an additional ten seconds to determine whether the ball is at rest. If by then the ball has not fallen into the hole, it is deemed to be at rest. If the ball subsequently falls into the hole, the player is deemed to have holed out with his last stroke, and he must add a penalty stroke to his score for the hole; otherwise, there is no penalty under this Rule.
In summary, you have the time it takes to walk to the ball plus 10 seconds. If it falls in after this time, the ball is holed but you add a shot.
A quick example
Your third putt comes up short and the golf ball lies on the edge of the cup. You walk to the ball, wait 10 seconds and it doesn’t fall in. After 20 seconds it falls in. You finish with a four.
And next time, hit it harder.