(a) For purposes of this article, except for scheduled injuries as provided in Section 25-5-57(a)(3), compensation for the first three days of disability shall not be payable, nor shall compensation be paid in any case unless the employer has actual knowledge of the injury or is notified thereof within the period specified in Section 25-5-78.
(b) Compensation shall begin with the fourth day after disability, and if the disability from the injury exists for a period as much as 21 days, compensation for the first three days after the injury shall be added to and payable with the first installment due the employee after the expiration of the 21 days. If any installment of compensation payable is not paid without good cause within 30 days after it becomes due, there shall be added to the unpaid installment an amount equal to 15 percent thereof, which shall be paid at the same time as, but in addition to, the installment.