You gotta come out every twenty to thirty minutes to expose the glans to oxygen.
Not sure that is correct. After all you can stay in a vacextender for 60 mins and the same principle applies. My glans does not seem too much worse for wear after 60 mins, However I do start to feel soreness in the cylinder around 60 mins but some of this seems to come from stretch pain closer to the base. With the dynamic air pump I started feeling soreness after 30 mins which is when I stopped.
With the Mr Fantastic water pump I use hot water, as hot as my penis can take. With the glans protector on I can tolerate it hotter as my glans is by far my most sensitive (to heat) part.