Trying to fetch all the RDS CA certificates as a bundle, and inspect them:

#!/usr/bin/python3
# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4
import urllib.request
import re
from OpenSSL import crypto
from datetime import datetime


def get_certs():
    url = ("https://s3.amazonaws.com/rds-downloads/"
           "rds-combined-ca-bundle.pem")
    with urllib.request.urlopen(url=url) as f:
        pem_certs = []
        current_cert = ''
        for line in f.read().decode('utf-8').splitlines():
            current_cert = current_cert + line + "\n"
            if re.match("^-----END CERTIFICATE-----", line):
                pem_certs.append(current_cert)
                current_cert = ""
        return pem_certs


def validate_certs(certs):
    ca = None
    for cert_pem in certs:
        cert = crypto.load_certificate(crypto.FILETYPE_PEM, cert_pem)
        if cert.get_issuer().CN == cert.get_subject().CN:
            ca = cert
    for cert_pem in certs:
        cert = crypto.load_certificate(crypto.FILETYPE_PEM, cert_pem)
        start_time = datetime.strptime(
            cert.get_notBefore().decode('utf-8')[0:14], "%Y%m%d%H%M%S")
        end_time = datetime.strptime(
            cert.get_notAfter().decode('utf-8')[0:14], "%Y%m%d%H%M%S")
        print("%s: %s (#%s) exp %s" %
              (cert.get_issuer().CN, cert.get_subject().CN,
               cert.get_serial_number(), end_time))
        if end_time < datetime.now():
            print("EXPIRED: %s on %s" % (cert.get_subject().CN,
                                         cert.get_notAfter()))
        if start_time > datetime.now():
            print("NOT YET ACTIVE: %s on %s" % (cert.get_subject().CN,
                                                cert.get_notBefore()))
    return

pem_certs = get_certs()
validate_certs(pem_certs)

Output

Today this gives me::

Amazon RDS Root CA: Amazon RDS Root CA (#66) exp 2020-03-05 09:11:31
Amazon RDS Root CA: Amazon RDS ap-northeast-1 CA (#68) exp 2020-03-05 22:03:06
Amazon RDS Root CA: Amazon RDS ap-southeast-1 CA (#69) exp 2020-03-05 22:03:19
Amazon RDS Root CA: Amazon RDS ap-southeast-2 CA (#70) exp 2020-03-05 22:03:24
Amazon RDS Root CA: Amazon RDS eu-central-1 CA (#71) exp 2020-03-05 22:03:31
Amazon RDS Root CA: Amazon RDS eu-west-1 CA (#72) exp 2020-03-05 22:03:35
Amazon RDS Root CA: Amazon RDS sa-east-1 CA (#73) exp 2020-03-05 22:03:40
Amazon RDS Root CA: Amazon RDS us-east-1 CA (#67) exp 2020-03-05 21:54:04
Amazon RDS Root CA: Amazon RDS us-west-1 CA (#74) exp 2020-03-05 22:03:45
Amazon RDS Root CA: Amazon RDS us-west-2 CA (#75) exp 2020-03-05 22:03:50
Amazon RDS Root CA: Amazon RDS ap-northeast-2 CA (#76) exp 2020-03-05 00:05:46
Amazon RDS Root CA: Amazon RDS ap-south-1 CA (#77) exp 2020-03-05 21:29:22
Amazon RDS Root CA: Amazon RDS us-east-2 CA (#78) exp 2020-03-05 19:58:45
Amazon RDS Root CA: Amazon RDS ca-central-1 CA (#79) exp 2020-03-05 00:10:11
Amazon RDS Root CA: Amazon RDS eu-west-2 CA (#80) exp 2020-03-05 17:44:42