If the title changes every second, this watcher sends data to the server, but the duration is 0.

Reproducible via:

let count = 0;

function updateTitle() {
  count++;
  document.title = `Count: ${count}`;
}

setInterval(updateTitle, 1000);

Hm ok, the issue seems to not be related to rounding, but to duration of last event not being updated before new one get's created, so it stays at initial value (zero):