I agree, I would love to know the logic behind that 20 hour calculation. The Cheeki Rafiki crew were experienced, knew something was wrong with their yacht, may well have been in dry suits, if not should have had time to get into immersion suits, should have had time to check the liferaft was clear to deploy and had time to trigger 2x satellite beacons some time apart. It would be very unlucky for all four of them to have been simultaneously incapacitated such that none either found sanctuary under the hull or were able to get into the liferaft.