Sounds like you need to keep text from appearing in this field until Field 1 receives a date.
Case ( Field1 > Field2 ; "OK" ;
Field1 ; "Not Ok )
This will return "OK" if there is a date in field 1 and it is greater than the value of Field2. It will return "not OK" if there is a value in Field1 and it is not greater than Field2. If field1 is empty, no value is returned and the field will be empty.