Convert a GTFS time (seconds since the start of the service day, as returned by parseGtfsTime) into a unix epoch in seconds.
Seconds since the start of the service day (may exceed 86400)
Service date in YYYYMMDD format
IANA timezone name of the agency
Convert a GTFS time (seconds since the start of the service day, as returned by parseGtfsTime) into a unix epoch in seconds.