Clarify that TTL is optional and doesn't override validity.

index.html

@@ -920,13 +920,13 @@ <h3>BitstringStatusListCredential</h3>
             <tr>
               <td id="ttl">credentialSubject.ttl</td>
               <td>
-The `ttl` indicates the "time to live" in milliseconds. This property MAY be
-present. If not present, implementers MUST use a value of `300000` for this
-property.  A verifier MUST NOT use a cached `BitstringStatusListCredential` that
-was cached for more than the `ttl` duration prior to the start of verification
-operation on a [=verifiable credential=]. Implementations that publish the
-status list SHOULD align any protocol-specific caching information, such as the
-HTTP `Cache-Control` header, with the value in this field.
+The `ttl` is an OPTIONAL property that indicates the "time to live" in
+milliseconds before a refresh SHOULD be attempted. If not present, no default
+value is assumed. The value does not override or replace the
+<a data-cite="VC-DATA-MODEL-2.0#validity-period">validity period</a>
+of the `BitstringStatusList`. Implementations that publish the status list
+SHOULD align any protocol-specific caching information, such as the HTTP
+`Cache-Control` header, with the value in this field.
               </td>
             </tr>
           </tbody>