320.If an employer fails to pay his assessment before the twenty-first day of the month following that of the mailing of the notice of assessment, he shall pay interest on that amount from the fifth day after the date of mailing of the notice.
320.If an employer fails to pay his assessment within the prescribed time, he shall pay, as interest, 5% of the unpaid amount for the first month of delay and the interest on that amount for subsequent months of delay.