src/main/java/com/conveyal/gtfs/GTFSFeed.java
public ZoneId getAgencyTimeZoneForStop (String stop_id) {
        StopTime stopTime = getStopTimesForStop(stop_id).iterator().next();

        Trip trip = this.trips.get(stopTime.trip_id);
        Route route = this.routes.get(trip.route_id);
        Agency agency = route.agency_id != null ? this.agency.get(route.agency_id) : this.agency.get(0);

        return ZoneId.of(agency.agency_timezone);
    }
public ZoneId getAgencyTimeZoneForStop (String stop_id) {
        StopTime stopTime = getStopTimesForStop(stop_id).iterator().next();

        Trip trip = this.trips.get(stopTime.trip_id);
        Route route = this.routes.get(trip.route_id);
        Agency agency = route.agency_id != null ? this.agency.get(route.agency_id) : this.agency.get(0);

        return ZoneId.of(agency.agency_timezone);
    }
Get the likely time zone for a stop using the agency of the first stop time encountered for the stop.