The standard time of your game is at your selected home airport.
So the times at the top of your schedule are the times at this airport.
If the timezone differs at the airport you are scheduling a flight to or from it will show this:
when you hover the flight it shows the local time in [] brackets next to the time of your home airport.
example:
I'm playing with British Airways. My home airport is London Heathrow. (this is the airport I selected when creating the game)
The times in yellow will always be UK time.
The times in red will show the local time. This only shows up if the time is different from UK time.
We will make this more intuitive in TAP NG. It needs some tweaking.