def _created_on_to_timestamp_ms(created_on):
    """
    Converts the Message CreatedOn column to a millisecond timestamp value.

    CreatedOn is number of 100 nanosecond increments since midnight 0000-01-01.
    Output is number of millisecond increments since midnight 1970-01-01.
    """
    return created_on / 10000 - 62167219200000