def change_interval(self, value):
        """ :param value: list of strings in format 'Day_of_Week-HH:MM' """
        assert not isinstance(value, string_types)
        self.timestamps = []

        for timestamp in value:
            event = EventTime(timestamp)
            self.timestamps.append(event)
:param value: list of strings in format 'Day_of_Week-HH:MM'