Only on Monday user can enters the data in any one of the table. - DBMS (Trigger)

create or replace trigger t4 before delete or insert or update on empmaster

begin

if (to_char(sysdate, 'day')not in('monday'))or(to_char(sysdate,'hh:mi')not between'08:30'

then  raise_application_error(-20001, 'table is secured ');

end if;

end;