Example: The times T1 and T2 are given by T1 = 6 hours 34 minutes 56 seconds and T2 = 2 hours 51 minutes 45 seconds.
Add the two times
Let S = T1 + T2 = (6 hours 34 minutes 56 seconds) + (2 hours 51 minutes 45 seconds)
add hours together, minutes together and seconds together
S = (6 + 2) hours (34 + 51) minutes (56 + 45) seconds = 8 hours 85 minutes 101 seconds
We now need to convert 85 minutes to hours : 86 minutes = 1 hour 25 minutes and 101 seconds to minutes: 101 seconds = 1 minute 41 seconds; and substitute
S = 8 hours 85 minutes 101 seconds = 8 hours + (1 hour 25 minutes) + (1 minute 41 seconds) = 9 hours 26 minutes 41 seconds

Subtract T2 from T1
With the subtraction, it might be easier to convert each time into seconds, subtract and convert again into hours, minutes and seconds.
T1 = 6 hours 34 minutes 56 seconds = 6 × 3600 seconds + 34 × 60 seconds + 56 seconds = 23696 seconds
T2 = 2 hours 51 minutes 45 seconds = 2 × 3600 seconds + 51 × 60 seconds + 45 seconds = 10305 seconds
Let D = T1 - T2 = 23696 seconds - 10305 seconds = 13391 seconds
Convert 13391 seconds into hours
D = 13391 seconds / 3600 = 3.71972222222 hours = 3 hours + 0.71972222222 × 60 minutes = 3 hours 43.1833333333 minutes = 3 hours 43 minutes 0.1833333333 × 60 seconds = 3 hours 43 minutes 11 seconds

How to Use the Degree Calculator

1 - Enter the times T1 and T2 in hours, minutes and seconds form, check your input and press "Add / Subtract". The outputs are the sum T1 + T2 and the difference T1 - T2 in two forms: hours, minutes, seconds and also in decimal hours.
Example of times T1 and T2
5 hours 34 minutes 23 seconds
0 ° 23' 56" (time less than 1 hour)