Need help subtracting and doing if statements for time

I would like to subtract two different times in the HH:MM format from an excel sheet and to then use result to use in a if statement where I will compare the resultant time from the substraction to another period of time, lets say 30 minutes.

Answer 1

[Steven Lord]

There doesn't seem to be any date information included with your data, so I'd use duration instead of datetime. I'm mostly using your data but I also wanted to show how I'd handle midnight crossings.

du = duration(["6:30", "7:30"; "8:30", "9:30"; "9:00", "10:00"; "17:45", "1:00"], ...
    'InputFormat', 'hh:mm')

du = 4×2 duration array
   06:30:00   07:30:00
   08:30:00   09:30:00
   09:00:00   10:00:00
   17:45:00   01:00:00

difference = du(:, 2)-du(:, 1)

difference = 4×1 duration array
    01:00:00
    01:00:00
    01:00:00
   -16:45:00

In this case the last difference is negative, which suggests that the flight was in the air at midnight. So let's add 24 hours to that entry.

inAirAtMidnight = difference < hours(0) 

inAirAtMidnight = 4×1 logical array
   0
   0
   0
   1

difference(inAirAtMidnight) = difference(inAirAtMidnight) + hours(24)

difference = 4×1 duration array
   01:00:00
   01:00:00
   01:00:00
   07:15:00

Note that I was able to use < between the duration array difference and the duration array returned by hours(0) to perform some comparisons.

Alternately we could have modified du directly. I made a copy of du as du2 in case you wanted to run the code and experiment yourself.

du2 = du;
departure = du2(:, 1);
arrival = du2(:, 2);
arrivedBeforeDeparture = arrival < departure

arrivedBeforeDeparture = 4×1 logical array
   0
   0
   0
   1

du2(arrivedBeforeDeparture, 2) = du2(arrivedBeforeDeparture, 2) + hours(24)

du2 = 4×2 duration array
   06:30:00   07:30:00
   08:30:00   09:30:00
   09:00:00   10:00:00
   17:45:00   25:00:00

difference2 = diff(du2, [], 2)

difference2 = 4×1 duration array
   01:00:00
   01:00:00
   01:00:00
   07:15:00

[Yassin Wahby]

I was trying for 2 hours and this instantly worked, thank you very much!