I have a large order spreadsheet listing orders placed by customers. There
are three date columns. Column K is the date the customer would like the
product delivered, column L is the date that is quoted by the system and
column M is the acknowledged delivery date from the supplier.

I would like to set up a system whereby if the date in any of the three
columns is nearby (say by 14 days), then that cell is flagged in yellow to
alert me to chase the delivery, but when the date becomes 7 days away, the
cell colour becomes red to really alert me to chase the delivery.

There is also a column (O) which is the despatch date. What I would like to
happen is for the three columns above to flag with an approaching date, but
as soon as I enter a date in the despatch date column (column O), the other
three fields stop being red.

Can I do this?