3. Format
Cells
Select the Number page
and choose Time from the category list.
select 13:30:55 from the options.
4. Calculate the duration
Select F2
and type this equation:
=INT(((E2-C2)*1440))/60
where E is the End Time column and C is the Start Time column.
Double click on the Auto fill handle and the equation will be copied
to the rest of the Duration column.