> If it says the certificate for your bank is expired, you need to stop.

No I don't. At least not if it's recent. A certificate that expired in the last month is roughly equal in safety to a certificate that's valid for another month or two.

Expiration is a backup safety measure and the risk is mostly based on how long it's been since the certificate was issued.

Unless any banks are going around leaking keys right after they expire for some weird reason?