1. OT rate for daily rated worker, you can seek guidance from the following clause in section 60i of the EA. In short, you use the average earnings of the previous month.
(1C) Where an employee is employed on a daily or an hourly rate of pay or on piece rates, the ordinary rate of pay shall be calculated by dividing the total wages earned by the employee during the preceding wage period (excluding any payment made under an approved incentive payment scheme or for work done on any rest day, any gazetted public holiday granted by the employer under the contract of service or any day substituted for the gazetted public holiday) by the actual number of days the employee had worked during that wage period (excluding any rest day, any gazetted public holiday or any paid holiday substituted for the gazetted public holiday).
2. For monthly rated workers, it is simpler: (salary/26/8) x 1.5