[#2208] updated documentation for timestamp-format

doc/sphinx/arm/hooks.rst

@@ -739,6 +739,30 @@ The lease-client context can only be printed using the default format, as this
 information is not directly stored in the request packet or in the response
 packet.
 
+The ``timestamp-format`` parameter can be used to change the timestamp logged
+at the beginning of each line. Permissible formatting is the one supported by
+strftime. The default is: "%Y-%m-%d %H:%M:%S %Z". This parameter has no effect
+for the database backends, where the timestamp is defined at the schema level.
+
+Examples:
+
+.. code-block:: json
+
+    {
+        "Dhcp6": {
+            "hooks-libraries": [
+                {
+                    "library": "/usr/local/lib/kea/hooks/libdhcp_legal_log.so",
+                    "parameters": {
+                        "path": "/var/lib/kea/log",
+                        "base-name": "kea-forensic6",
+                        "timestamp-format": "%l%t%w %F%%"
+                    }
+                }
+            ]
+        }
+    }
+
 Additional parameters for the database connection can be specified, e.g:
 
 .. code-block:: json