Being addicted to the gym is a bad thing. Seriously!
People who are addicted to the gym often focus on the wrong things: being proud of doing more work NOT on getting more results.
They become stimulus addicts, always trying to do more and more work.
While I admire people who are hard workers, you must understand that the ONLY purpose of training is to improve your body (make it more muscular, leaner, stronger, more healthy). Doing more work should only be a goal if it will lead to more progress.
And the fact is that rest days are important for maximum growth and performance improvements.
LISTEN I was a stimulus addict. I was the guy who tried to train everyday. And since I'm pretty smart I was able to find logical reasons to justify training everyday, often twice a day. But in doing so I severely limited my progress over the years.
The sad thing is that with the people I train I always use 4 or 5 training days per week. But with myself I used to do 6 or 7. My clients actually progressed a lot faster than me!!!
I'm in contact with a lot of very strong and large people. Powerlifters, strongman competitors, bodybuilders. And out of all the high level strength athletes I know, 4 days of lifting a week is the norm. And with bodybuilders it's either 4 or sometimes 5. Even the top Crossfit athletes I work with do 4 or 5 days a week. Why would people with elite genetics for heavy work be able to only train 4 or 5 days a week but those with lesser genetics be able to train every day, sometimes twice a day? It doesn't make sense.
I recently went back to training 4 or 5 days a week and my strength progress is A LOT faster... and I'm talking SHOCKING fast.
NOW the 20 minutes routine is low volume. So in theory, yeah you might be able to "do it" twice a day, everyday. But I honestly believe that it would be a mistake. First because I think that you will not get more progress, and you might actually get less. But also because it will reinforce a psychological problem and will make it worse.
Do what you want, but I cannot condone what you want to do.