Parse a GTFS time string into seconds since the start of the service day.
Accepts "HH:MM:SS" and lenient variants ("H:MM:SS", "HH:MM"). Hours may
exceed 24, so the result may exceed 86400. Returns undefined for
missing or malformed input (e.g. interpolated stop times with no value).
Parse a GTFS time string into seconds since the start of the service day.
Accepts "HH:MM:SS" and lenient variants ("H:MM:SS", "HH:MM"). Hours may exceed 24, so the result may exceed 86400. Returns
undefinedfor missing or malformed input (e.g. interpolated stop times with no value).