I think you should see this video from earlier this year at the European Tour:
Clement Sordet was putting for a birdie… but did he get the birdie or did he not?
The Rules of Golf (Rule 13.3a) states this:
If any part of a player’s ball overhangs the lip of the hole:
- The player is allowed a reasonable time to reach the hole and ten more seconds to wait to see whether the ball will fall into the hole.
- If the ball falls into the hole in this waiting time, the player has holed out with the previous stroke.
- If the ball does not fall into the hole in this waiting time:
- The ball is treated as being at rest.
- If the ball then falls into the hole before it is played, the player has holed out with the previous stroke, but gets one penalty stroke added to the score for the hole.
So the big question is, what “a reasonable time” is.
Interpretation 13.3a/1 states this:
Determining the limits of a reasonable time to reach the hole depends on the circumstances of the stroke and includes time for a player’s natural or spontaneous reaction to the ball not going into the hole.
How long can this reaction time be? That is not determined.
Probably Sordet’s reaction time is considered “reasonable”. Therefore the 10 seconds started when he reached the hole, and since the ball fell into the hole a few seconds after, it was holed without penalty – thus he got his birdie.
If a reaction time is not reasonable, the 10 seconds starts after what is considered a “reasonable time”.