When you fly to directly connected flight path (ex. Dalaran → Argent Tournament) then the flight time is displayed correctly, it is not the case when you fly to a place via other flight paths (ex. Dalaran → via Argent Tournament → via The Shadow Vault → Death's Rise) then the time will be shown incorrectly, and the bars will finish mid flight.
I can't know for sure, but I have an assumption on why is it happening: I think it doesn't stack the time needed to fly from each individual places together and counts them separately, which causes this error. What I mean it is counts the time to get from Dalaran to Argent Tournament as one bar but at the same time in the second bar it starts counting the time it takes from Argent Tournament to The Shadow Vault, it does not account for the time it takes to get from Dalaran to Argent Tournament. Again, it is just an assumption and I can't be sure, but seeing that it says it takes 4 minutes to fly from Dalaran to the flight masters at the ends of the Northrend it is certainly wrong.
When you fly to directly connected flight path (ex. Dalaran → Argent Tournament) then the flight time is displayed correctly, it is not the case when you fly to a place via other flight paths (ex. Dalaran → via Argent Tournament → via The Shadow Vault → Death's Rise) then the time will be shown incorrectly, and the bars will finish mid flight.
I can't know for sure, but I have an assumption on why is it happening: I think it doesn't stack the time needed to fly from each individual places together and counts them separately, which causes this error. What I mean it is counts the time to get from Dalaran to Argent Tournament as one bar but at the same time in the second bar it starts counting the time it takes from Argent Tournament to The Shadow Vault, it does not account for the time it takes to get from Dalaran to Argent Tournament. Again, it is just an assumption and I can't be sure, but seeing that it says it takes 4 minutes to fly from Dalaran to the flight masters at the ends of the Northrend it is certainly wrong.