This research investigates the impact of prolonged oxygen deprivation (approximately 40 minutes) on foundational cognitive capacities such as attention, declarative memory, and executive control. Data was analyzed from twenty one participants under normoxic and hypoxic conditions performing the psychomotor vigilance test, a paired associates task, and the change signal task. Hypoxia delayed simple visual response times and reduced response inhibition throughout the entire protocol. On the scale of minutes, false starts tended to increase across blocks when participants were hypoxic, but this effect did not carry across blocks. Finally, declarative memory performance was initially unaffected. However, after approximately 20 minutes, hypoxia nearly reversed gains from the first 20 minutes while performance under normoxic conditions continued to improve. The results show a differential susceptibility of different cognitive processes to hypoxia at different time scales and support the use of PVT as a diagnostic for decrements attributed to hypoxia.