Your response does NOT address the problem you have or that I am reporting, since use of GMT is just fine and would NOT prevent you from correctly calculating the estimated flying time.
If you post the time for Beijing in GMT and the time for the flight in Vancouver as PST, that still permits you to calculate the total scheduled flight time correctly, but you are not doing that!
There are 7 hours difference between PST and GMT, and the flight itself shows a time of 4 hours and x minutes, so since the flight is heading WEST you ADD the 7 extra hours to the 4 hours and 52 minutes to get the correct ESTIMATE of 11 hours and 52 minutes SCHEDULED flight time.
It has nothing to do with the failure to have the correct time zone for Beijing… It has EVERYTHING to do with what you are saying is the scheduled flight time, which is WRONG, and there is NO excuse for that error, since you do NOT need the time zones for those airports not in the US or Canada.
For the airports in the US or Canada, use GMT as THEIR time for all your calculations and you will always get the correct total estimated travel time since the time zone changes will be eliminated from the computation!
Convert the Vancouver time to GMT and THEN calculate the estimated flight time. You will get the correct travel time in the air, since both airports will be using the same time zone for the start and end of the flight. Just make certain you correctly account for the DIRECTION of travel, which in this case is WESTBOUND, across the international date line.
Or build a simple table, Beijing is at +8 hours to GMT while Vancouver is at -7 hours to GMT, so the difference is, going west, 9 hours in time zone changes and going east it is 15 hours in time zone changes, and you could still calculate the scheduled trip time correctly.
The aircraft leaves Vancouver at 19:40GMT and lands at 8:05GMT the next day. so we add 8 hours and 4 hours and we add 5 minute and we add 20 minutes and we get an estimate of 12 hours and 25 minutes between departure and arrival, and NOT the 4 hours and 50 odd minutes you show on your site as the ESTIMATED flight time!
Do not bother telling me why the above cannot be done, since you already have ALL of the time zone information you need even if you do NOT know the correct time zone for Beijing.