The answer is in two parts – getting to the hole and waiting.
You are allowed a reasonable time to reach the hole and then a further 10 seconds to wait and see.
More about the rule a golf ball overhanging the hole
Specifically, this is rule 13.3
If the ball drops into the hole but the 10 seconds of waiting has passed you are required to add one penalty stroke to your score.
The video below is a great example of how the rule can be bent by a slow walk, a stare, a slow process of taking a stance. Note, in our eyes Zach J. was not intentionally bending the rules but his actions may have broken them. The commentators talk of applying a penalty but we're not clear on the final outcome.
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