The validity shows the date until which your order remains valid if it is not executed right away. You can choose a day order, valid only on trading days until the stock exchange closes, or a date in the future (end of next month by default) (=good till date).

As validity, do not select a day order when the stock exchange is already closed or on stock exchange closing days as your order will not be executed.

Do not confuse a day order (= validity) with a market order (= order type). A market order is executed immediately during market hours.