When a company declares a dividend, three dates matter:
The declaration date is when the board announces "we'll pay X DZD per share."
The ex-dividend date (or ex-date) is when the share starts trading WITHOUT the right to that dividend. If you buy the share on or after the ex-date, the previous owner keeps the dividend. To collect it, you need to hold the share on the trading day BEFORE the ex-date.
The payment date is when the cash actually lands in shareholders' accounts — typically two to six weeks after the ex-date.
On the Calendar page, dividend events are stamped with the ex-date because that's the day the share price drops by roughly the dividend amount, and it's the cutoff for entitlement. The payment date is informational.