When I was playing a game a lady started counting down, I thought I was in byoyomi, so I played, then after the next move she continued counting down.
I hadn’t actually finished main time, and the lady was counting down that.
Is it necessary to count down at the end of main time?
My personal feeling is that it is not necessary, only counting down in byoyomi is necessary, although a notification when you enter byoyomi would be useful too.