The SUM function - Adds up columns or rows of numbers. Click on the Date Time option on the ribbon to open the list of date functions. Excel Basic Functions Entering Values.
Meaning your Sum formula should include at least 1 number reference to a cell or a range of cells.
Use Excels built-in number formats to format the date and time produced by the NOW function to your desired format. Discover how functions in Excel help you save time. Type the equals sign then enter the function name SUM for example. Typing a formula inside the cell.