Southwest award cancellation policy and refund qustion

Hi,

Question about Southwest cancellation policy. My parents have a tight transfer connection flight from UA to Southwest. In case if they are not able to make their Southwest connecting flight (booked with points), can they cancel their SW flight 30 min prior (even though they already check-in the SW flight and have the boarding pass) the flight departure time and receive points and tax fee refund? When is the latest they can cancel the SW award flight and receive full refund?

Also, if the award if booked within 24 hours of departure time, is it also eligible to receive full refund of points and tax? For example, if the flight is booked today at 3 pm and the flight is cancelled at 1 pm tomorrow.

Thanks