models.py

# sample code as a suggestion for https://convore.com/django-community/how-to-make-an-automatic-status-change/

from datetime import datetime

class MyManager(models.Manager):
    def active(self):
        return self.get_query_set().filter(expires_at__gt=datetime.now())

class MyClass(models.Model):
    created_at = models.DateTimeField(auto_now_add=True, db_index=True)
    expires_at = models.DateTimeField(db_index=True)
    
    @property
    def active(self):
        return self.expires_at > datetime.now()