After defeating the boss, complete darkness sets in, and then normal time returns.

I'm pretty sure that's intentional. It's gives a pretty cool feeling, and also emphasizes the fact that the moon cycle has been reset, and that's the new newmoon (if that's intentional)

1 hour ago, DaZoul said:

...also emphasizes the fact that the moon cycle has been reset, and that's the new newmoon (if that's intentional)

it is

5 hours ago, DaZoul said:

I'm pretty sure that's intentional. It's gives a pretty cool feeling, and also emphasizes the fact that the moon cycle has been reset, and that's the new newmoon (if that's intentional)

To be honest, I don't know if it was a mistake or not, but it seemed to me at that moment that something went wrong. For example, maybe it was some kind of end of every night with full moon or the beginning of permanent darkness.