Unique slugify with time in unix

import time

class Offer(models.Model):
    title = models.CharField(max_length=140,)
    description = models.TextField(max_length=500, blank=True, null=True)
    slug = models.SlugField(max_length=240, unique=True)
    created_at = models.DateTimeField(auto_now_add=True, editable=False)

    def __str__(self):
        return self.title

    def save(self, *args, **kwargs):
        new_slug = slugify(self.title)
        Klass = self.__class__
        if Klass.objects.filter(slug=new_slug).exists():
            slug_str = '%s %s' % (self.title, str(time.time()).strip('.')[1:])
            self.slug = slugify(slug_str)
        else:
            self.slug = new_slug
        super(Offer, self).save(*args, **kwargs)