If you want to round the Log in and out times within their own cells, you will need to use VBA. Alternately, you can have Excel round them internally while performing calculations on them.

Also, your bio says you are using 2003 but this is at least a 2007 worksheet. Will this need to be 2003 compatable? Will it be saved as an xls file or an xlsm (workbooks containing vba cannot be xlsx files)