Isolating the max date for a date and time stamp

Hi,

I appending warehouse data on an hourly basis so we can see warehouse activity by hour by day by week and so on.  I am trying to build a filter or indicator that will allow me to filter the most current timestamped date only when needed.  I am using the below beastmode and it's not working.  Any suggestions as I thinking I might be missing something in Magic that I can use to achieve this "flag".  I want to use all the reports sometimes and then just reference the most current other times. 

case
   when TIMESTAMP(`Report Time Stamp`) = max(TIMESTAMP(`Report Time Stamp`))
      then 'Y'
               else 'N'
end

Any help would be amazing!

Thank you all!