Any day on which an employee regularly or customarily performs any work for a covered employer shall be deemed a normal workday. Normal workdays for purposes of computing daily disability benefits shall be the number of workdays usual to the employment in which the employee is or was last employed before disability. In the absence of such a normal workweek, or in the case of employees entitled to collect benefits from the special fund in accordance with the provisions of section 207 of the Workers' Compensation Law, the normal workweek shall be deemed to be Monday to Friday inclusive.