Box change depending on drop-down list validation

Question

For this example, we will use the top line of data so...

Type = H6 
Time Depart = I6
Time landed = J6
Single Engine In Command = K6
Single Engine Dual = L6

My plan is to add I6 and J6 into L6 if H6 says Dual. But I6 to add with J6 into K6 if H6 says In Command.

Can anyone help me with my boxes? In L6 I already have the formula (to make box blank if no values in I6 & J6;

=IF(AND(I6<>"", J6<>""), J6-I6, )

Answer 1

=ARRAYFORMULA({IF((I6:I<>"") * (J6:J<>"") * (H6:H=K$5), TEXT(J6:J-I6:I, "hh:mm"), ), 
               IF((I6:I<>"") * (J6:J<>"") * (H6:H=L$5), TEXT(J6:J-I6:I, "hh:mm"), )})

demo spreadsheet