Well, there are two ways you can do this....
1)
Put this script in the crontab and set it to run everyday.
Something like this:
#!/usr/bin/ksh -p
# Check for leap year.
cal 2 `date "+%Y"`|grep 29 1> /dev/null 2>&1
if [ $? -eq 0 ]
then
DAYS=366
else
DAYS=365
fi
# Get ANS here.
let ANS=${DAYS}-`date "+%j"`
echo "Days till Dec. 26th: ${ANS}\n" > /etc/motd
# Add whatever else goes here, such as a standard message.
cat STANDARD_MESSAGE >> /etc/motd
That should work or something similar...the following could also be done...
2)
Edit /etc/skel/.profile to include the above entry to get the number of days till Dec. 26th and then just copy the .profile scheme to all of the home directories.
Add this after the message:
echo "Days till Dec. 26th: ${ANS}\n"
read PAWS?"Press [Enter] to continue."
clear
Either one of these solutions could work depending on your setup.