title: Filter model object by difference in days
body: <p>My model has a date field and i want to filter the model by the last 7 days.</p>
  
  <pre><code>class Count(models.Model):
      task = models.ForeignKey(Task, related_name = 'counts', on_delete = models.CASCADE)
      start_time = models.DateTimeField(null = True, blank = True)
      end_time = models.DateTimeField(null = True, blank = True)
      time_spent = models.PositiveIntegerField()
      deleted = models.BooleanField(default = False)
  
      class Meta():
          ordering = ['accesses']
  
      def __str__(self):
          return f'{self.task.department} - {self.accesses.first().user} [{self.time_spent} min]'
  
      def stamped_date(self):
          if not self.start_time:
              return self.accesses.first().date
          return self.start_time
  
      def users(self):
          return list(set(map(lambda x: x.user, list(self.accesses.all()))))
  </code></pre>
  
  <p>I need to filter every count that has "stamped_date" in the last 7 days.</p>
  
  <p>What i tried to do (in the model):</p>
  
  <pre><code>    def daysBy(self):
          return (datetime.now() - self.stamped_date()).days
  </code></pre>
  
  <p>to filter like this:</p>
  
  <pre><code>Count.objects.filter(daysBy__let = 7)
  </code></pre>
  
  <p>However, datetime.now() requires a timezone object, otherwise will throw the follwing error:</p>
  
  <pre><code>TypeError: can't subtract offset-naive and offset-aware datetimes
  </code></pre>
  
  <p>I'm also feeling this might not be the most correct way of achieving my goal, please correct me with a better way.</p>
  
  <p>Or.. give me a way of inserting a timezone object related to the TIME_ZONE setting.</p>