Because he cannot find enough food for himself and his younger sister, a 14-year-old Haitian boy attempts to prepare a meal from unripe Ackee fruit. He and his sister are found hours later by other refugees, who transport them to a rural aid station. The patients present with frequent vomiting and intermittent loss of consciousness in the sister. The toxin in Ackee fruit converts carnitine and coenzyme A into nonmetabolizable esters, effectively shutting down long-chain fatty acid oxidation. The lack of substrate inhibits gluconeogenesis, leading to hypoglycemia. Gluconeogenesis becomes the main source of blood glucose after approximately ___ hours of fasting.