Hmm, this is not impossible, but rather unlikely... Did you make sure to change the power button setting? I don't remember how it is named exactly but I belive it's necessary to get it work. Also you could try to separate adb command for two and use superuser access:
Code:
adb shell
su
settings put secure lock_screen_lock_after_timeout 86400000
Many thanks my friend! This really helped: "Did you make sure to change the power button setting? I don't remember how it is named exactly but I belive it's necessary to get it work"
This made me remember, that the above adb commands probably just increase the time to auto lock the screen.. If you press the button it lock instantly bypassing this I think.. So i setup auto lock the screen in 15 sec (without pressing the button), and is working. When screen goes of automatically, it supposed to lock in 5 sec i think, if you don't preen the power button during this 5 sec (otherwise it will auto lock after those 5 sec). Now this 5 sec has become a day..

So tablet stay unlocked and when i press the power key it goes to desktop. Let's hope tablet go to standby and not consuming battery this way.. This one needs to test.
I think i had an app which just turn screen off without lock. Or probably i can do it in tasker, i will try. I think it's going to work this way.. Or perhaps there is a setting when press the power button not to lock instantly. I don't remember if there is, I'll search it.
Thanks again!
Edit. I just made a command in tasker: turn screen of (without checking lock) and it works.. Screen goes of without locking (normally it won't lock for 5 sec i think, but now is for a day). So i can "lock" by a button shortcut in screen, without really lock, or i can press the button and lock instantly with locksceen (which needs fingerprint to unlock).. Or i can set to double press the power button to run the tasker shortcut, so pressing the power button screen of and lock the tablet, or double press the power button to turn the screen off without lock.. I have the choice.. It's ok this with me, many thanks again!!