Adding Times

You can add times using the "+" operator or by using the SUM function.
However Excel will not add more than 24 hours.
When the time exceeds 1 it rools to the next day
To force Excel to stay on the same day you can use on the following custom number formats:
[h]:mm:ss
'37:30:25

It is possible to add times together using the normal + operator only when the total number of hours is not greater than 24.
If the total time is more than 24 hours then this approach will not work.
If you add up 8:00, 9:00 and 10:00 using a normal formula you will get the result 3:00 which is obvously not right.
Excel defaults to displaying times in 24hr notation so (8 + 9 + 10 = 27) = 3 in a 24hr notation.

If cell A1 contains a true date and time then:
to get the date component use INT(A1)
to get the time use A1-INT(A1) or MOD(A1,1)
to find the difference between two dates use DATEDIF(A1,A2,"d")