borderline nocturnal
Staying up so late over winter/spring/summer break that you are sleeping through almost the whole day.
Todd: Dude, I've been texting you all day, why didn't you answer?
Mike: Sorry bro I've been so borderline nocturnal lately that I couldn't check my phone until now.
Mike: Sorry bro I've been so borderline nocturnal lately that I couldn't check my phone until now.