VoG - thanks for response one minute!! I have also tried formatting the total as (h:mm) but it returns a result such as ) 0.30 when the answer is obviously several hours. I wondered it something happened if it went over 24 hours?
You must enter the time using a colon to seperate the hours:minutes:seconds (depending on which components of time you are using)
VoG™'s comment is correct. To rephrase it slightly, there is no such "time" as 25 o'clock, which is what you're trying to achieve by formatting as "time". What you seek is a "duration". as VoG™ siad, format the cells using a custom format;
15 hours plus 10 hours will give the followiing results...
h:mm equals 1:00
hh:mm equals 01:00
[h]:mm equals 25:00
[hh]:mm equals 25:00
depending on you exact calculations,you may aslo find that you have to either multiply of divide your figures by 24 to convert to/from days to hours.
The following 2 sites, (2nd courtesy of vog), are excellent sources of info and explanation for time calculations;