def getMsgTime(line):
    """Parse the timestamp off the 978 message and return as a float.

        Args:
            line (str): Line containing a 978 message with a timestamp at the end.

        Returns:
            float: Timestamp of the message.

        Raises:
            Exception: If the timestamp can't be found.
    """
    payloadTimeIndex = line.find(';t=')

    if payloadTimeIndex == -1:
        raise Exception('Illegal time format')

    timeInSecs = float(line[payloadTimeIndex + 3:-1])

    return timeInSecs