Fix duration being calculed by created time when not started yet

Author: kkthxbye-code

netbox_script_manager/models.py

@@ -167,7 +167,7 @@ def serialize_object(obj, resolve_tags=True, extra=None):
 
     @property
     def duration(self):
-        start_time = self.started or self.created
+        start_time = self.started
 
         if not start_time:
             return ""