unix_field.py

class UnixEpochDateField(serializers.DateTimeField):

    def to_representation(self, value):

        """ Return epoch time for a datetime object or ``None``"""

        if type(value) is time:
            d = date.today()
            value = datetime.combine(d, value)

        try:
            return time_a.mktime(value.timetuple()) * 1000
        except (AttributeError, TypeError):
            return None

    def to_internal_value(self, value):
        return datetime.fromtimestamp(value // 1000).replace(second=0)
    
    
    
    
    class CalendarSerializer(RemovableSerializerFieldMixin, serializers.ModelSerializer):
    activity = serializers.PrimaryKeyRelatedField(queryset=Activity.objects.all())
    initial_date = UnixEpochDateField()
    assistants = serializers.SerializerMethodField()
    schedules = HTMLField()
    packages = CalendarPackageSerializer(many=True, required=False)

    class Meta:
        model = Calendar
        fields = (
            'id',
            'activity',
            'initial_date',
            'enroll_open',
            'session_price',
            'assistants',
            'is_weekend',
            'is_free',
            'available_capacity',
            'note',
            'schedules',
            'packages',
        )
        depth = 1

I noticed there was an issue with the UnixEpochDateField when it came to TimeZone aware objects.
I found the fix and put up a gist: https://gist.github.com/hammadzz/fe8f35c4b4344dd6ce9f73d23e825c96