ServicenotificationQuery: Apply query optimization from NotificationhistoryQuery

refs #9009

modules/monitoring/library/Monitoring/Backend/Ido/Query/ServicenotificationQuery.php

@@ -66,6 +66,18 @@ class ServicenotificationQuery extends IdoQuery
         )
     );
 
+    /**
+     * {@inheritdoc}
+     */
+    public function whereToSql($col, $sign, $expression)
+    {
+        if ($col === 'UNIX_TIMESTAMP(sn.start_time)') {
+            return 'sn.start_time ' . $sign . ' ' . $this->timestampForSql($this->valueToTimestamp($expression));
+        } else {
+            return parent::whereToSql($col, $sign, $expression);
+        }
+    }
+
     /**
      * {@inheritdoc}
      */