The date validation page does not correctly validate entered dates on this page if the Global Option is set to "DD/MM/YYYY" format.
If the entered 'Day' value is larger than 12 AND the Global Option for "System Date Format" is set to "DD/MM/YYYY" this warning will be seen.
WORKAROUND: Change the System Date Format to MM/DD/YYYY to create or edit any "Message of the Day" dates.
STATUS: This has been addressed in TPAM version 2.5.919.
From the 2.5.919 Release Notes section "Resolved Issues":
"If the Global Setting date format is set to DDMMYYYY, there are issues with start and end dates for Message of the Day.