Here's how you can create a dropdown list of times in Microsoft Excel:

1. Select the cell where you want to create the dropdown list.
2. Go to the "Data" tab in the Excel ribbon and click on "Data Validation".
3. In the "Data Validation" dialog box, select "List" from the "Allow" dropdown menu.
4. In the "Source" field, enter the following formula:
   Formula:

   =TIME(ROW(A1),0,0) 

5. Click "OK" to close the dialog box.

This formula will create a list of times in 1-minute intervals from 12:00 AM to 11:59 PM. The ROW(A1) part of the formula generates a series of numbers from 1 to 1440 (the number of minutes in a day), and the TIME function converts those numbers into time values.

Now, when you click on the cell with the dropdown list, you should see a list of times to choose from. You can also copy and paste this dropdown list to other cells in your worksheet.