I don't even see where flightstats.com says there is a "schedule change" for UA 840 SYD-LAX on September 26.

From To Departure Arrival Status Equip. Set
Code City Code City Scheduled Actual Scheduled Actual Alert
UA 840 MEL Melbourne SYD Sydney 11:15 AM 11:15 AM 12:35 PM 12:35 PM Scheduled
Ontime 744
UA 840 LAX Los Angeles JFK New York 11:30 AM 07:49 PM Scheduled
Ontime 757
UA 840 SYD Sydney LAX Los Angeles 01:45 PM 01:45 PM 10:14 AM 10:29 AM Scheduled
Ontime 744