Came across a lit review recently on hypoxic training that suggests 2hrs 2/week may be insufficient to elicit adaptations.
Sinex & Chapman, 2015. Hypoxic training methods for improving endurance exercise performance
Exposure to sufficiently high altitude (2000–3000 m) for more than 12 h/day, while training at lower altitudes, for a minimum of 21 days is recommended.
However a more recent study found beneficial effects in swimmers from 6 weeks of 3 days/week of 120min/day of what sounds like a mix of continuous and high intensity interval training.
Park et al, 2018. Efficacy of intermittent hypoxic training on hemodynamic function and exercise performance in competitive swimmers
So… your mileage may vary?