Dahua Camera Times - How close from Cam to Cam?

Techie007L said:
Yes, the camera times are always within a second on all of my Blue Iris installations. Some use the router as the time source (when the cameras are on the network with a router I provided), and others use the Blue Iris PC as the time source (when the cameras are on their own private network). I typically use the slowest NTP interval permitted by the cameras (30 minutes, 60 minutes, and 1440 minutes seem to be common figures).
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Will give your script a try.

Ran both w32tm /query /configuration and w32tm /query /status on the BI windows computer. The results are in the text file.

Take a look and let me know if there is anything unusual going on. The NTP server on the router updates the BI computer. The cams are updated via the BI system clock.

There is always the possibility that something else is going on.
 

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Looks good; the only thing I can't see there is verifying your firewall rule (and do note the Public/Private network designation that can affect how the firewall applies the rules). Make sure your PC's IP address is entered and NTP turned on on the cameras. A quick test would be to turn off NTP on a camera, nudge its time by a few minutes, hit [Save], and then turn NTP back on with an interval of 1 minute. The camera's time should visibly correct itself within a minute of hitting [Save] again (some cameras do it as soon as you hit [Save], others do it after the time elapses).
 
Based on what I said, the OP said he tested some cams and some showed being off time within seconds, so it really doesn't matter if there is a slight delay from a NTP and all this other trouble shooting going on.

Some of the cameras just plain suck at holding time.
 
Cameras shouldn't be drifting seconds apart within an hour; after days/weeks/months with no synchronization, sure. Every time I've seen my cameras seconds apart, it's because NTP time synchronization had been broken for some reason for an extended period of time. Hence the test in my previous post. That said, I will add that if NTP is confirmed working and your cameras still are ending up seconds apart, reduce the synchronization period—if 1440 minutes, to 60 minutes. If 60 minutes, to 30 minutes, or even 10 minutes if a camera is really bad. But I haven't seen this be necessary—I've got cameras holding split-second accuracy syncing only every 24 hours! Also, I will note that there was a certain version of the 5442 firmware that broke automatic NTP synchronization several years back (I don't remember the version number).

On a more technical note, I have observed that a camera system will typically start out with split-second accuracy (i.e. all the cameras click seconds by at the same moment). However, because the cameras synchronize on an arbitrary timer (every XX minutes since last sync) rather than on the clock (i.e. on the :00 of the hour), they will often come apart over time—especially if any cameras have rebooted since power-on. I discovered that this occurs due to the parent device (i.e. a router) resynchronizing its time in response to the (now out-of-group) NTP request from a device. Jitter over the Internet causes millisecond discrepancies in the parent device's clock, which are then passed on to the requesting device. If all the camera's NTP requests were always grouped together (as they are from a cold power on, and would remain if they made their requests say on the hour), this would not occur as they would all be pulling their time from the same NTP synchronization of the parent device.
 
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