I've prepared a workbook to answer your dilemma.
You need three things.
1) A field that determines the status of the time - is it overtime, regular time, etc.
2) A Parameter that lets the user select to see overtime, regular time, or all time
3) A calculated field based on this parameter in (2) that uses field (1)
Because the field in (1) splits the data into two parts (overtime and regular) and the parameter gives an option for selecting all the time but you want to view this aggregated you will need to use the additional caculution to be able to reference one, the other, or both parts of the field.
Working Day Hours.twbx 11.7 KB