Investors who hold shares of the company in their demat account on the record date announced by the company are eligible to receive split shares. 

Under the current T+1 settlement framework, the ex-date and record date are generally the same for corporate actions. So, to be eligible, you should buy the shares 2-3 days before the ex-date/ record date. 

If you buy the shares on or after the ex-date, you will usually not be eligible for that particular stock split.