Document periodic tasks and timezones. Closes #543

docs/userguide/periodic-tasks.rst

@@ -157,6 +157,42 @@ The syntax of these crontab expressions are very flexible.  Some examples:
 |                                         | every hour during office hours (8am-5pm).  |
 +-----------------------------------------+--------------------------------------------+
 
+.. _beat-timezones:
+
+Timezones
+=========
+
+By default the current local timezone is used, but you can also set a specific
+timezone by enabling the :setting:`CELERY_ENABLE_UTC` setting and configuring
+the :setting:`CELERY_TIMEZONE` setting:
+
+.. code-block:: python
+
+    CELERY_ENABLE_UTC = True
+    CELERY_TIMEZONE = "Europe/London"
+
+.. admonition:: Django Users
+
+    For Django users the timezone specified in the ``TIME_ZONE`` setting
+    will be used, but *not if the :setting:`CELERY_ENABLE_UTC` setting is
+    enabled*.
+
+    Celery is also compatible with the new ``USE_TZ`` setting introduced
+    in Django 1.4.
+
+.. note::
+
+    The `pytz`_ library is recommended when setting a default timezone.
+    If :mod:`pytz` is not installed it will fallback to the mod:`dateutil`
+    library, which depends on a system timezone file being available for
+    the timezone selected.
+
+    Timezone definitions change frequently, so for the best results
+    an up to date :mod:`pytz` installation should be used.
+
+
+.. _`pytz`: http://pypi.python.org/pypi/pytz/
+
 .. _beat-starting:
 
 Starting celerybeat