The numbers below are a pretend dashboard drawn from a 4 KB snapshot inlined in this page. How fast they appear is one of the measurements.
Ready.
Follow-up: ~2 min and ~65 MB on Wi-Fi, ~1.5 min on cellular. One device at a time, with this page in front.
Reset this browser's test state (if a run got stuck)
One manual step. Tap Start, then switch to another app (or lock the screen) for at least 30 seconds, then come back here.