Hi, Heroku engineer here. We rekeyed our certificates, including the one for *.herokuapp.com, meaning we resent our original certificate requests (CSR) to our CA but signed with new private keys. This is why the dates didn't change.
Our CA will eventually revoke the previous incarnations of our certificates, signed with the old private keys, making them invalid.
Our CA will eventually revoke the previous incarnations of our certificates, signed with the old private keys, making them invalid.