in relation to a penalty that arises on a particular day (for example a late filing penalty) or interest on that penalty, the beginning of that day, and
mewn perthynas â chosb sy’n codi ar ddiwrnod penodol (er enghraifft, cosb am ffeilio’n hwyr) neu log ar y gosb honno, dechrau'r diwrnod hwnnw, a