LibreOffice Calc: How to get total for HH:MM:SS cells
It's a matter of formatting the cells. You will have to apply the format code [HH]:MM:SS. It's already predefined:
(Screenshot from LibreOffice 3.4.3)
Very often the time value is presented as a string ie. appears as '01:00:00 when formatted as time.
There are two solutions to this:
To delete the single quote. This is extremely tedious if there are more values
To create another cell which uses a formula to convert to timevalue. If eg A1 contains '01:00:00 then create another cell with =TIMEVALUE(A1), the formula can be dragged along to easily convert multiple values