Netflow - (currently, I have 566 expired IP Addresses)

After working with NPM for years, I am new to NTA.

I was going through my Netflow Settings and came across this:

DNS and NetBIOS Resolution

     Maximum time spent to process IP addresses:

          Custom number of minutes [60] (currently, you have 566 expired IP Addresses)

Is this supposed to be clearing them out and it is not?

or

Is it telling me that I have a bunch I need to find and remove?

Thanks in advance. -