I'm not really sure about the 20 minute of active rest. I guess it would have to be something that required minimal concentration as you need that 20 minute rest period to let your brain compute everything.It's funny, 20 minutes A DAY was what my parents made me practice on clarinet growing up and I think I became quite good over 8 years, probably better than on bass after 25 years as an adult with all the usual life junk!
Here's another trick and this is scary how well this works. When I'm trying to work on technically demanding stuff I'll play for a while then once I'm confident in the movement I'll lie down on the floor and visualise my hands going to the correct places etc going through all the movements and then once I stand back up to play again I'm more confident and much more accurate. Again it's all to do with the brain. If we stand upright (or sit) then there's a lot of background work being done by the brain to keep us up which takes away what we can focus on. If we lie down, the floor is doing that job and the brain doesn't have to so our concentration levels go up. It's actually a very useful technique when I'm trying to memorise something or trying to commit an un-natural movement to my muscle memory. Slightly scary how well it works. Maybe that would be a good way of doing active rest?