It is unclear whether you mean Diwali bonus and statutory bonus under the Payment of Bonus Act as the same.
There is no Diwali bonus under the Act. It is just that organizations choose to pay statutory bonus on the eve of Diwali.
Under the Act every employee who has worked for 30 days in the financial year is eligible to receive bonus whether working or resigned.
Employees drawing salary up to 21000/-pm are eligible but the bonus is payable only on salary of 7000/-pm or minimum wages for the industry/skill level whichever is higher.
Minimum bonus % is 8.33% and maximum is 20%.
Bonus is payable within eight months' from the close of financial year.
Ex-gratia payment is outside the scope of the statutory bonus and its eligibility to receive by the ex-employees is left to the management's decision.