def extract_digest_key_date(digest_s3_key):
    """Extract the timestamp portion of a manifest file.

    Manifest file names take the following form:
    AWSLogs/{account}/CloudTrail-Digest/{region}/{ymd}/{account}_CloudTrail     -Digest_{region}_{name}_region_{date}.json.gz
    """
    return digest_s3_key[-24:-8]
