Question

Why the Stamina/Prey Boost reduce two minutes instead of one minute when you start using it?

Answer 1

That's a design feature intended to avoid abuses. First of all, it's clear that it wouldn't make sense to only decrease a second at a time when the player gets experience, otherwise 1 hour would last for a much longer duration since during hunts you spend a lot of time attacking and not receiving any experience.

The choice of 2 minutes was probably made as a middleground to avoid abuses (i.e. players making their stamina last longer than intended) but also fair. In my personal experience when teamhunting each pull lasts between 40 and 60 seconds (depending a lot on various factors, of course), which means that 2 minutes will always be enough to ensure the system is not being abused.