Is the time on the play-stone accurate in relation to timeout?

I was playing a game today, and I was concentrating on a ko whilst in in my last period of byo-yomi. Not looking at the clock, I was instead going by the number shown on the play-stone which indicates how many seconds one has remaining. When I timed out, I’m pretty sure that it told me I still had something like four seconds remaining. Perhaps I’ve remembered wrongly, but if anyone would take a quick look at the code I’d appreciate it.