Canceling a nonrefundable fare will result in an eCredit for the full amount paid (minus any cancellation fees, depending on fare type and route). However, if you cancel a refundable ticket, you'll get the amount paid refunded back to your original form of payment.
How long do I have before I cancel my flight?
within 24 hoursThe 24-hour rule is a regulation from the US Department of Transportation that says airlines must offer either free 24-hour price hold (so you can lock in the price and purchase within 24 hours) or free cancellation for 24 hours.