The latest impl is in catapult-csm: 
https://github.com/catapult-project/catapult-csm/blob/breakdownMapper/tracing/tracing/metrics/system_health/time_to_interactive.html#L131

Detecting network quietness design doc and proposal:
https://docs.google.com/document/d/1y6NYcI2NyLMh88KVr2NaevdX2e-e03vL99Wn-gy_hVk/edit

Edge case example:
https://github.com/GoogleChrome/lighthouse/issues/2447

Goals:
0.3: Publish doc on evaluation procedure.
0.3: Evaluate 3 candidates.
0.4: Land successful candidate in catapult