Scott, Steve, and every other Z2 proponent have done a great job getting their methodologies to the masses- no doubt about it. I've read, love, and purchased copies of them for our own clients and group.
But, this is far less about there being some magic formula/training zone and more about the sum of the parts: find the right mix of easy, moderate, and hard over time. Assuming that's above what you've already been used to doing- and it sounds like much of this concept is brand new to some of us- and you'll reap a noticeable reward. Sure, more is better, but that might also mean 2-3-4 hours leading into your hunt reaps massive rewards if you've been doing none of this up until now.
A single 8-12 week block may look like this:

You can see where this is WAY above what the usual way.
You can see where it was gradual- not a linear rocket ship up to 2x the volume.
You can see where there were periods of recovery for a week to absorb the volume.
(If you could zero in further) you would see where this is WAY below the "ideal" volume "needed" for Z2 to "work".
Even though not "ideal" (15-20 hours), you can see where practical is still
highly effective when above your norm:

The second year of training like this carried further than my first because there was a base to build from. There are some more thoughts and ideas included in the image and the arrows.
Also, Z2 proponents aren't saying "never do hard, high-intense workouts!" They're saying there is a place, time, and reason to add those, but they're not
the thing (as many have been accustomed to believing).
Strength training and recovery as vital parts too as they're the foundation in which ALL this volume rests.
Having a plan is great, but knowing flexibility IN that plan is important too or you end up with diminishing returns from turning the jets on too much.
TLDR: It goes without saying that 20-minutes won't put you in "Zone 2". At the same time, don't let the recommended volume scare you away from trying it at all. Keep the general rule of thumb, challenge your normal dedicated time to fitness (i.e. give a little more time to it than usual), but still make it realistic. Be consistent. You'll reap the reward.
PS: This thread epitomizes when it's worth hiring a coach. A decent understanding of the basics doesn't mean a high degree of confidence and certainty. A good coach will help you navigate your questions and provide explanation in a way that makes you understand it so well that you couldn't NOT buy in. The difference is then have a high degree of confidence what what you're doing will work and
that makes the work easier to commit to.