Added validation for timezones

erpnext/crm/doctype/timezone/timezone.py

@@ -3,8 +3,12 @@
 # For license information, please see license.txt
 
 from __future__ import unicode_literals
-# import frappe
+import frappe
 from frappe.model.document import Document
 
+
 class Timezone(Document):
-	pass
+    def validate(self):
+        if self.offset > 720 or self.offset < -720:
+            frappe.throw(
+                'Timezone offsets must be between -720 and +720 minutes')