diff --git a/cms/envs/common.py b/cms/envs/common.py
index cd92f17b1d..9d246edece 100644
--- a/cms/envs/common.py
+++ b/cms/envs/common.py
@@ -201,7 +201,7 @@ STATICFILES_DIRS = [
 TIME_ZONE = 'America/New_York'  # http://en.wikipedia.org/wiki/List_of_tz_zones_by_name
 LANGUAGE_CODE = 'en'  # http://www.i18nguy.com/unicode/language-identifiers.html
 
-USE_I18N = True
+USE_I18N = False
 USE_L10N = True
 
 # Localization strings (e.g. django.po) are under this directory
diff --git a/common/lib/xmodule/xmodule/combined_open_ended_module.py b/common/lib/xmodule/xmodule/combined_open_ended_module.py
index e01ae49149..74082df1ce 100644
--- a/common/lib/xmodule/xmodule/combined_open_ended_module.py
+++ b/common/lib/xmodule/xmodule/combined_open_ended_module.py
@@ -8,7 +8,7 @@ from .x_module import XModule
 from xblock.core import Integer, Scope, String, List, Float, Boolean
 from xmodule.open_ended_grading_classes.combined_open_ended_modulev1 import CombinedOpenEndedV1Module, CombinedOpenEndedV1Descriptor
 from collections import namedtuple
-from .fields import Date
+from .fields import Date, Timedelta
 import textwrap
 
 log = logging.getLogger("mitx.courseware")
@@ -229,7 +229,7 @@ class CombinedOpenEndedFields(object):
         default=None,
         scope=Scope.settings
     )
-    graceperiod = String(
+    graceperiod = Timedelta(
         help="Amount of time after the due date that submissions will be accepted",
         default=None,
         scope=Scope.settings
diff --git a/common/lib/xmodule/xmodule/fields.py b/common/lib/xmodule/xmodule/fields.py
index dc2f000286..b7094203c4 100644
--- a/common/lib/xmodule/xmodule/fields.py
+++ b/common/lib/xmodule/xmodule/fields.py
@@ -82,6 +82,9 @@ TIMEDELTA_REGEX = re.compile(r'^((?P<days>\d+?) day(?:s?))?(\s)?((?P<hours>\d+?)
 
 
 class Timedelta(ModelType):
+    # Timedeltas are immutable, see http://docs.python.org/2/library/datetime.html#available-types
+    MUTABLE = False
+
     def from_json(self, time_str):
         """
         time_str: A string with the following components:
diff --git a/lms/envs/common.py b/lms/envs/common.py
index 0579fc94d6..f4ecb318f6 100644
--- a/lms/envs/common.py
+++ b/lms/envs/common.py
@@ -378,7 +378,7 @@ FAVICON_PATH = 'images/favicon.ico'
 # Locale/Internationalization
 TIME_ZONE = 'America/New_York'  # http://en.wikipedia.org/wiki/List_of_tz_zones_by_name
 LANGUAGE_CODE = 'en'  # http://www.i18nguy.com/unicode/language-identifiers.html
-USE_I18N = True
+USE_I18N = False
 USE_L10N = True
 
 # Localization strings (e.g. django.po) are under this directory