immature welcome to the QR forum. Most of your questions will have answers hidden away somewhere in the forum. The dashboard is a good place to start looking around.

The general rule is that check-in for a flight at out-stations starts three hours before departure. There are a few exceptions but very few. CPH is not one of them.
Check-in for QR164 at 22.40 opens at 19.40 and not before.