Airplane

The airplane departs from city $A$ at h_1 hours m_1 minutes (local time of city $A$) and arrives in city $B$ at h_2 hours m_2 minutes (local time of city $B$).

From city $B$, it departs at h_3 hours m_3 minutes (local time of city $B$, possibly on another day) and returns to city $A$ at h_4 hours m_4 minutes (local time of city $A$).

The flight duration is the same in both directions (not equal to $0$). How long does one leg of the flight take? Write the answer in hours and minutes, rounding up to the nearest minute if necessary.