To convert a time value to a decimal, you can simply change the format. But it isn't so easy to convert a value that represents a measurement of time.
- Select the data (A1:F15).
- Choose Subtotals from the Data menu. Excel will default to the Date value in column A for changing.
- If necessary, choose Sum from the Use Function drop-down list.
- In the Add Subtotal To list, check both Total and Decimal (you want subtotals for both columns).
- Click OK.