sum the hours in crystal

I have a report which displays hours (eg 1:33 ) worked by each employee on a job grouped by date.
I need to display the total hours on each day. How can I sum the hours in crystal using a formula or some other way possible. I need the total in hours and minutes .
thx for your help

What is the datatype of the Hours field?

It is a calculated field using datediff of two dates and converting it into the hours:minutes format. In Crystal this field is showing as string.