You may cancel your reservation within 24 hours from the time of original booking for a Refund to the original form of payment.

Travel must be booked seven days or more prior to your scheduled departure date and the entire booking must be cancelled.

But how they work to know you must read this blog

Click on JetBlue Cancellation Policy.
https://medium.com/@AirlinesBooking/jetblue-cancellation-policy-1-844-313-7010-28197a025755