from django.utils import timezone

now = timezone.now()
active_bookings = Booking.objects.filter(
    start_time__gte=now,
    end_time__lt=now
)

# myapp/models.py
class Booking(models.Model):

    @property
    def is_active(self):
        now = timezone.now()
        return self.start_time >= now and self.end_time < now

# In your view or in a utility function
myBooking = Booking.objects.get(id=12345)
print(myBooking.is_active)

# myapp/management/commands/update_active_bookings.py

from django.core.management.base import BaseCommand

class Command(BaseCommand):

    def handle(self, *args, **kwargs):
        now = timezone.now()
        for booking in Booking.objects.all().iterator():
          is_active = self.start_time <= now and self.end_time > now
          if self.is_active != is_active:
            # Only saving the model if we have to
            self.is_active = is_active
            self.save()

*/10 * * * * source /path/to/venv/bin/activate && /path/to/app/manage.py update_active_bookings