Do signed topology transactions expire?

Is there any TTL or “valid until” on a signed topology transaction or proposal? Or can a transaction signed today, e.g. a NamespaceDelegation or the next-serial PartyToParticipant, be held and submitted weeks later, as long as the serial still matches? Is the serial the only replay protection?

If a namespace key was briefly misused (e.g. unauthorized KMS Sign), can signatures from that window be invalidated without moving to a new namespace?