@classmethod
def datediff(cls, dt_start, dt_end=None):
    """
        Get difference in millis between two datetime
        :param dt_start: Start datetime
        :type dt_start: datetime.datetime
        :param dt_end: End datetime (will use current utc if not provided)
        :type dt_end: datetime.datetime
        :return float
        :rtype float
        """
    if dt_end:
        delta = dt_end - dt_start
    else:
        delta = cls.datecurrent() - dt_start
    return (delta.days * 86400 + delta.seconds
        ) * 1000 + delta.microseconds * 0.001
