'Convert a time formatted string to a float.
:param time_string: time formatted string
:returns: a timestamp as a float'

@classmethod
def _convert_time_string_to_float(cls, time_string):

    time_object = timeutils.parse_isotime(time_string)
    return (timeutils.normalize_time(time_object) - datetime.datetime.utcfromtimestamp(0)).total_seconds()
