It is important to establish that when someone's snap score goes up, the only thing you can know for sure is that they are sending/receiving someone's snaps.
Understand Your Snapchat Score!
This is because the snap score of an account on Snapchat is based on how many snaps they have sent and received. This also means that their snap score is not solely based on how many snaps they have sent to someone. You also can't be sure what kind of snaps they're sending, for example, they might be hanging out with a friend.
As for why it seems to happen late at night, it could be due to time constraints such as their friend working all day and not being able to keep in touch via snaps; therefore, they would have to chat with them outside of working hours.
That being said, there are many possible reasons why they stop talking to someone in the late hours. While it's easy to jump to conclusions, it doesn't always mean they have something or someone to hide.
