|Read the Excel Help File (or Google) for Conditional Formatting.|
You can use the TODAY() function in a Rule and compared it to the 10th of each month to format the cell. However, in order to make the cell flash, I believe that you are going to need VBA. See here:
I also don't understand how you plan to use Paid in E1. Once you enter Paid in E1 to stop the flashing, are you planning on deleting it so that you can enter it again next month? That doesn't sound like a good way to accomplish your goal.
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