External Real Time Clock option - No cloud access

I got my C-7 Nov22 and have been very happy w/ it. I recently lost grid power at night, so my UPS kept the hub up for 2hours until it ran out (unscheduled shut down is not good). Grid power and internet was out for 3 days. I'd run the house off a generator, shutting the hub down, then the house, at night. Restarting the generator at 7am.
Now the issue. When the hub booted up, the internal RTC was off, w/ the last date/time, so it set the wrong mode. All my automations are based on time of day and proper modes (morning/day/afternoon/evening/night). Obviously this is a problem, and I needed to set the proper date/time from a browser. This blows me away there is no coin cell battery powered RTC inside the hub.
That being said, is there a work around that can poll a local device upon boot while there is no internet available?
I've searched previous posts, that go way back, and have been closed.

Yes, you will need an NTP server on your network and can then set the hub to use that server instead of a cloud NTP server. See:

It's often helpful to share what you've found. Closed posts are not necessarily bad; many of these were done as part of a cleanup a while back. The advice may still be correct, but if you already tried something and had a problem and what you tried was still a current method of doing so, there may be another problem.


Thank you bertabcd1234. After posting this, I did see the avail app to set time based on a local server. DUH!
Not being up on internal servers at home, I was really hoping for something simpler.
Looks like I'll be doing something like

I have a TalentCell battery powering my hub that I've tested out to 5 days. The hub would keep time as long as it was still powered, even without Internet, no? The hub uses very little power, and the generator would keep the battery topped up.

Also, in my area, sometimes even though hardwire internet is lost, mobile internet still works, for a while at least, so a phone could be used as a hotspot.

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I use a TimeMachines TM1000A for my entire network. Pricey, but rock solid.


While it likely works, it should be noted that the app is a different approach from what I linked to above.

The other replies also made me realize I should mention: this isn't something I do myself. I also have mine on a UPS, where it can last for (at least) hours without mains power. This eliminates many concerns, loss of time if the hub comes back up before my network after a power outage being one (though most of that is also on a UPS so either is rare).

For a similar capability to @jwjr I'm running a Raspberry Pi with a GPS hat, a $23 external GPS antenna and a nice case. The pi runs ntpd, referenced to the GPS. Its been running in my basement since 2019. The antenna is in one of my window wells.

$75 maybe?



Thanks everyone! Ya'll are the best! I'm learning a lot.

The hub’s internal clock can drift if it has no NTP server to sync with. But over a period of a few days, I believe it would be minimal.