Nightstand Mode
Sadly, Nightstand Mode doesn’t take advantage of the always-on display at all. In some ways this is only a little bit surprising, as this is something that Apple likely could have added years ago; since Nightstand mode only engages when the Apple Watch is actually on the charger, battery life isn’t an issue here.
However, on the Apple Watch Series 5, Nightstand mode works in the exact same way as on prior Apple Watch models. The screen will automatically shut off after a predetermined time interval, so you won’t be able to simply wake up and glance at the time like you could from a bedside clock, although it does come on when it detects any motion at all, so a simple nudge of your bedside table is usually enough to light it back up, and just like with older Apple Watch models, if you have an alarm set, it will gradually illuminate as your wake-up time approaches.
It’s unclear why Apple has chosen to not extend its always-on display to Nightstand mode, although it’s possible that there’s a technical reason for it related to screen life or screen burn. It’s worth noting, however, that if you wear your Apple Watch to bed, the screen will remain on just like it does when you’re wearing it during the day.