JetBlue’s 24-hours cancellation policy:

Customers can amend or cancel their airline tickets within 24 hours of the original purchase date, as long as it is done before 7 days before the flight's departure, without incurring any additional fees. You must incur Cancellation fee if you stay longer than that window of time.

Note:

Reservations made through JetBlue Vacations are not covered by this policy.
This specific policy does not apply to the changes under this category.

Also check : Southwest Flight cancellation fee