[Form] Add input_format option to TimeType

Author: fancyweb

reference/forms/types/time.rst

@@ -20,6 +20,7 @@ stored as a ``DateTime`` object, a string, a timestamp or an array.
 | | - `hours`_ |
 | | - `html5`_ |
 | | - `input`_ |
+| | - `input_format`_ |
 | | - `minutes`_ |
 | | - `model_timezone`_ |
 | | - `seconds`_ |
@@ -129,6 +130,16 @@ on your underlying object. Valid values are:
 The value that comes back from the form will also be normalized back into
 this format.
 
+input_format
+~~~~~~~~~~~~
+
+**type**: ``string`` **default**: ``H:i:s``
+
+If the ``input`` option is set to ``string``, this option specifies the format
+of the time. This must be a valid `PHP time format`_.
+
+.. _`PHP time format`: https://secure.php.net/manual/en/function.date.php
+
 .. include:: /reference/forms/types/options/minutes.rst.inc
 
 .. include:: /reference/forms/types/options/model_timezone.rst.inc