According to this paper, 8+ hours is adequate: "severe inadequate ...4.7 to 4.1 hours per night... moderate inadequate... (6.0 to 5.5 hours per night... , mild inadequate... 7.2 to 6.8 hours per night... and adequate... 8.4 to 8.0 hours per night."
Sleep duration/timing and glucose regulation in over 1,100 people with 14-day continuous glucose sensor tracking jamanetwork.com/journals/jam...