I have tasted today thoroughly both auto screen activation and keep screen on feature and realized that auto turn on timeout had preference over keep screen on. That means if both are activated, screen turns off after delay set in auto display activation dialog. I find it not too logical, I find more intuitive keeping screen always on if the switch is ON regardless on auto screen activation.
Second note to auto screen on generally - activation is working as expected except screen off which is acting unexpectedly, I've got screen offs immefiately after notification. The screen off interval is not yet working too well.