Any idea how to write a Validation Rule, that prevents the user from creating more than one record a day.

I have one Object called (Stundenkonto__c) it shows a Month in Timetracking. I have a Object called (Zeiteintrag__c) it is the Master Detail of (Stundenkonto__c) So the User should only be able to create only one (Zeiteintrag__c) Record a day.