Using @IsDate function will only tell you if a FIELD is in Time/Date format,
not if the value is valid. To properly validate that a text field has a valid
Time/Date value (when not originally specifying the field as Time/Date to begin
Convert the text value to time with @TextToTime. If invalid Time/Date, the
conversion will result in nothing!
@If(@Text(@TextToTime(DateField))= "";@Failure("Invalid Date");@Success)