Based on reading the guide you linked to, the author of the guide is proposing a house-rule to try to “fix” something he perceives as a problem with the Bloodhunter’s Order of the Mutant subclass.
To me, it seems like the guy who wrote the guide is rather missing the point, though.
…there’s little incentive to prepare (most mutagens) unless you can find out what you’re facing well ahead of time.
Well, yeah, that’s the whole concept of the subclass. The Order of the Mutant is largely based on The Witcher — and one of the main mechanics of the Witcher games (and of how Geralt operates in the novels) is that he has to do the footwork to understand what he’s facing and prepare for the fight before he goes in, waiting patiently and engaging only on his own terms. If he gets jumped or tries to skip the prep time, he’s going into the battle severely weakened.
To me that analysis sounds a lot like “It’s not fair that wizards have to prep their spells in the morning, so here’s a house rule that lets them just decide what spells they want later.” Sure, that powers-up the class, but it ruins the flavor of the thing.
Also, to be honest, I don’t actually see much of a difference between spending a minute or an hour to prepare mutagens, as far as the gameplay goes. It’s very rare that you have ten turns to spare getting ready and can’t spend an hour instead; usually you’re either immediately in combat and just have to deal, or you have the opportunity to withdraw and take some time to prepare first, which can be a few rounds or a whole short rest.