According to the NWA web site Customer First

Will I be able to hold my reservation if I want to explore other travel options?


If you purchase your ticket at the time you make your reservation, you can secure your ticket, the fare you've been quoted and a guarantee for a full refund without penalty fees if you cancel your reservation by the end of the next day (midnight Central Standard Time). If you don't cancel the reservation, however, you will not receive a refund unless you have purchased a fully refundable fare.

Suggestion is to buy the ticket now.... you can alway cancel!!