Snapshot -expiry-time is not what you'd think

Regularly scheduled snapshots cycle out whereas manually-created snapshots persist until auto-deleted (if configured) only when short on space or deleted manually.  There is a -expiry-time option for the volume snapshot create command but this counter-intuitively locks the snapshot to prevent deletion until that time.  Although I see the value in that feature, I think that option should be called something like -expiry-lock and instead -expiry-time should auto-delete the snapshot when specified.  Irksome.