I need three columns in a custom list that shows time only - such as 
check-in time; 06:00:00
 and checkout time; 06:45:24, 
I need to calculate the time differences in the third columns such as 00:45:24 - I need the third columns formate time as [hh]:mm: ss for analysis purposes if I need to show overall difference time such as the total time spend in whatever a place.