The eligibility of any corporate action depends on the Record date and Ex-date of the scrip.

What is the Record date and Ex-date?

Record date: The Record date is the cut-off date used to determine which shareholders of stock are entitled for a corporate action. On this date, the company checks the list of all the shareholders who own stock in that company and therefore are eligible for the bonus issue.

Ex-date: From this date, the shares of the company start trading without reflecting the benefits of corporate actions such as bonus issues, which means that shareholders should purchase shares before the ex-date to become eligible for bonus shares. 

For example, if the ex-date is 3rd Dec, then you can buy till 2nd Dec to be eligible for a Bonus. If you buy shares on 3rd Dec or after 3rd Dec, then you will not be eligible to receive Bonus.