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