Unmatched pending orders get canceled when the market closes, which is why if your order is left unmatched you get the message “exchange mass cancel.” The validity of unmatched orders is up until the market closes. Every unmatched order gets canceled post the following times mentioned in their particular segment.
Timings for every segment:
Commodities – 11:45 PM
Currency – 5:00 PM
Equity – 4:00 PM
If you have placed any orders that are unmatched on the exchange, in other terms, not executed, then the exchange cancels every pending order post market closure. In the next trading session, you will then have to place your orders again.