When does timing start? It could start on when start is let go, or first black frame, or time sense reset, or when you spawn or when you press start

Time starts on the first black frame.

(These all sound like reasonable options, but we wouldn't use "when you press start" because nothing happens until you let go, and "time since reset" is mostly a standard used by Japanese runners. It's not a bad idea, but North American runners have been using a different criterion for so long that there would be no good way to change over.)