I've noticed that the system time on my ER706W managed by an Omada software controller is consistently behind time.

I have enabled the NTP server in my site

But gateway configuration shows this device (ER706W) is not compatible with NTP. 

However if I change the time zone on the Site settings (change to another time zone and then back to my time zone) the gateway time is corrected, only for it to fall behind over the course of one minute.

The screenshot below is repeated terminal queries on the system time of the gateway ER706W after changing the time zone to another time zone and back again to my time zone. I'm running these queries approx once per second.  You can see the time is correct and then drop back where it remains around 20 seconds behind.

The behaviour is similar if I change the time on the server running the controller.

Can anyone help to understand and correct this behaviour?