Update policy description for SystemUse24HourClock policy.

chrome/app/policy/policy_templates.json

 {
 # policy_templates.json - Metafile for policy templates
 #
 # The content of this file is evaluated as a Python expression.
 #
 # This file is used as input to generate the following policy templates:
 # ADM, ADMX+ADML, MCX/plist and html documentation.
 #
 # Policy templates are user interface definitions or documents about the
 # policies that can be used to configure Chrome. Each policy is a name-value
@@ skipping 4095 matching lines @@
       'type': 'main',
       'schema': { 'type': 'boolean' },
       'supported_on': ['chrome_os:30-'],
       'device_only': True,
       'features': {
         'dynamic_refresh': True,
       },
       'example_value': True,
       'id': 236,
       'caption': '''Use 24 hour clock by default''',
-      'desc': '''Specifies the clock format be used for the device. Users can override clock format for the current session. However, on logout it is set back to the specified value. If an empty string is provided, device owner preference is used.''',
+      'desc': '''Specifies the clock format be used for the device.
+
+      This policy configures the clock format to use on the login screen and as a default for user sessions. Users can still override the clock format for their account.
+
+      If the policy is not set to true, the device will use a 24 hour clock format. If the policy is set to false, the device will use 12 hour clock format.
+
+      If this policy is not set, the device will default to a 24 hour clock format.''',
     },
     {
       'name': 'ShowLogoutButtonInTray',
       'type': 'main',
       'schema': { 'type': 'boolean' },
       'supported_on': ['chrome_os:25-'],
       'features': {
         'dynamic_refresh': True,
         'per_profile': True,
       },
@@ skipping 1455 matching lines @@
       'desc': '''Text appended in parentheses to the policy name to indicate that it has been deprecated''',
       'text': 'deprecated',
     },
     'doc_recommended': {
       'desc': '''Text appended in parentheses next to the policies top-level container to indicate that those policies are of the Recommended level''',
       'text': 'Default Settings (users can override)',
     },
   },
   'placeholders': [],
 }