I'd never had a phone with AOD until two weeks ago, and as soon as I tried Standby Mode it would still turn off after a few minutes. Better than 20 seconds that non-AOD phones could manage, but even so.
I prodded the screen, and it came on for a few more minutes. Prodded again, ditto. Prodded again and it stayed on all night.
It just needed to know I was serious (I was in a hotel and using it as an alarm clock).