One solution would be to put something like this formula in a cell adjacent (on the same row) to the "action taken" cell (assuming here that we're on the second row and the "action taken" cell is in column B):

Of course, you can change the number of days and the message, but essentially whenever the given number of days have passed, the message will be displayed. You can format the cell to display in red to make it more noticeable.

An alternate method would be to use Conditional Formatting on the "action taken" cells so that if the value of the cell is less than:

--the text of the action cell displays as red (or some other color, or a distinctive font, or whatever).