There are many ways to validate a date, but it looks like you're looking for a quick way to ensure that the user has entered 10 characters. You could verify on exit that the entry is 10 characters and then post a message if it isn't (using JavaScript):
if (this.rawValue.length != 10){
xfa.host.messageBox("errorMessage","errorTitle",0,0);
}
You can also set the value back to null if the user entered less than 10 characters if you really want to get the point across.
If you're looking for something more extensive, let me know.
Good luck with your deadline.