The "day-long night" from starting/ending the event goes away on relog

So, when you summon the Mysterious Energy, it turns the rest of the day into a full moon night. Similarly, killing the Celestial Champion turns the rest of that day into a new moon night.

If you log out during either of those "day long" nights, when you log back in, the day will once again be "normal" AKA separated into day, dusk and night (normal or enlightened).