The MOTD tool does not respect the "Specify Dates" selected in the availability section.
1. Access MOTD tool and create new annc
2. Select Specify Dates radio button and click Beginning and End date checkboxes
3. Enter a day later than today's date in the beginning box
4. Click Save Changes
5. Login as a non-admin user
6. You can still see the MOTD.
The workaround for now is to just HIDE the announcement until you're ready to display it.