models.py

class Day(models.Model):
    DAY_CHOICES = (
        ('SEG', 'Segunda'),
        ('TER', 'Terça'),
        ('QUA', 'Quarta'),
        ('QUI', 'Quinta'),
        ('SEX', 'Sexta')
    )
    day = models.CharField(max_length=3, choices=DAY_CHOICES, blank=False, 
    null=False, verbose_name="Dia da semana")

class Hour(models.Model):
    HOUR_CHOICES = (
        ('08:30', '08:30'),
        ('09:30', '09:30'),
        ('10:30', '10:30'),
    )
    hour = models.CharField(max_length=5, choices=HOUR_CHOICES, blank=False, 
    null=False, verbose_name="Horário")

class Student(models.Model):
    name = models.CharField(max_length=255, verbose_name='Nome Aluno')
    day_id = models.ForeignKey(Day, on_delete=models.CASCADE, null=True)
    hour_id = models.ForeignKey(Hour, on_delete=models.CASCADE, null=True)