如果只有登機和抵達時間, 可以計出兩地有時差的飛行時間嗎?

Yes assuming you can look up the time zones of the locations.

Duration = Arrival Time - Departure Time + (Time zone of from-location - Time zone of to-location)

Your example:
Duration = [06:00] - [23:35] + (GMT+8 - GMT+1)
= 30:00 - 23:35 + 7:00
= 29:60 - 23:35 + 7:00
= 13:25

2007-05-18 12:05:17 補充：
Sorry, 睇錯時間.Should be Duration = [06:30] - [23:35] (GMT 8 - GMT 1)= 30:30 - 23:35 7:00 = 29:90 - 23:35 7:00= 13:55

不可以。
沒有公式。

Yes , if you hv the 時差 then u can 計出兩地有時差的飛行時間 , but if you don't hv the 時差 then u can't 計出兩地有時差的飛行時間 , 當飛行時間是55分 , then 時差是6:00 , but 當飛行時間是1:55分 , then 時差是5:00 , so it don't hv 一條公式計飛行時間總共是多少個小時.

no, you question is that: one equcation but two unknowns. So can be solve uniquely.

Also, the flight time from A to B is different from B to A

以數論數：沒有、不可以