Should I enter Authentication Code if I am trying to clear validation details for the first time during a day?

No. While trying to clear validation details for first time, you will not have the Authentication Code, hence you are not required to enter this value. You can proceed by entering other details for validation on this screen (i.e., Token Number, CIN / BIN Details and PAN-Amount). On completion of validation, Authentication Code will be generated and displayed when you proceed to next page.