I noticed that too - closer to 15 seconds, I think. The clocks on the boxes do need to be synchronized periodically.
Ahh... 15 secs I would believe. I didn't really pay attention to when I stopped my watch, only that I knew it was after and therefore my watch time should be longer than my SI time, and was surprised to discover later that it wasn't.
What really struck me was yesterday when I didn't punch my watch at all, but was surprised when looking at my splits printout to find some legs unbelievably too short (by minutes) followed or preceded by other legs too long.
I guess sync-ing the boxes must be something people are good about doing before A meets but less disciplined about for local meets. It's not something I've ever noticed before and then suddenly noticed it 2 days in a row.
Oh wait! They just posted splits on AP of the HVO course yesterday and now I see what happened there. It wasn't clock sync at all. I punched one of the controls twice, almost 5 minutes apart, after losing contact with the map and relocating by returning to the previous control, which I spontaneously decided to punch again before continuing.
The splits posted on AP are correct and ignore the 2nd punch, but the splits from the receipt printer that I got at download are all off-by-one after the double punch at #11. It shows the 2nd punch of #11 as being #12, etc.