Should I be concerned about this

Generally, Malware would require the user ( you ) to be tricked into downloading some software from an Unknown or Untrusted Developers

Then, the user ( you ) would have to purposely and willingly install the software and giving the software access to bypass the Security Built into the Operating System.

As I said, it would be in the Applications folder if you downloaded and installed it. It was an app to switch from light mode to dark mode based on the time of day, or a schedule set by the user.

Only if you have that application installed on your Mac.

As KT stated, nothing to worry about unless you installed NightOwl yourself. I assume you would know whether you did or not. It would be in the Applications folder if you did.

FWIW, NightOwl didn't start as malware.

You're welcome.