s2s/keys: clarify minimum_valid_until_ts query

Signed-off-by: famfo <famfo@famfo.xyz>

data/api/server-server/keys_query.yaml

@@ -34,10 +34,10 @@ paths:
         - in: query
           name: minimum_valid_until_ts
           description: |-
-            A millisecond POSIX timestamp in milliseconds indicating when the returned
-            certificates will need to be valid until to be useful to the requesting server.
+            A millisecond POSIX timestamp. The returned keys SHOULD be valid
+            until at least this timestamp.
 
-            If not supplied, the current time as determined by the notary server is used.
+            If not supplied, the notary server SHOULD use the current time.
           required: false
           example: 1234567890
           schema:
@@ -98,12 +98,11 @@ paths:
                           type: integer
                           format: int64
                           description: |-
-                            A millisecond POSIX timestamp in milliseconds indicating when
-                            the returned certificates will need to be valid until to be
-                            useful to the requesting server.
+                            A millisecond POSIX timestamp. The returned keys
+                            SHOULD be valid until at least this timestamp.
 
-                            If not supplied, the current time as determined by the notary
-                            server is used.
+                            If not supplied, the notary server SHOULD use the
+                            current time.
                           example: 1234567890
               required:
                 - server_keys