US DOT requires airlines to provide either a 24 hold or free cancellation within 24 hours of booking except for certain close-in bookings.
https://www.transportation.gov/airco...ur-reservation
QR chooses to provide a 24 hold without payment.
From qr.com:
Note for flights from/to the US:
Bookings made for flights to or from the US can be held for 24 hours without payment. Once payment received and the ticket is issued, standard fare rules apply.
See also:
24 Hour Cancellation Policy