UPDATE: I did some experimenting with my cameras and found something interesting: If I go into the camera date/time configuration page and set the date to 2/26/2020, then click Save, it changes it to 2/27/2020. Entering 2/5/2020 and saving changes it to 2/6/2020. But if I enter 1/26/2020 and save, it remains at that date. If I enter 3/4/2020 and save it, it stays at that date. Basically, any date in February gets incremented when I save it. Dates in Jan or Mar (or other months) don't display the bug. I even tried Feb dates in 2019, and they also saved properly without adding a day. Finally, I tested other years, Feb dates always saved correctly without changing. Until I got to 2024. Then Feb dates were automatically incremented again after saving; but only Feb dates -- no other months.
So, these test results strongly suggest that this firmware has some type of bug when handling leap years, and in particular, any date in February in a leap year. Whenever my DVR syncs its internal date during February, it sends it to the cameras to update them, and they increment it (by two days) and show the wrong date. Looking back at Feb footage, all recordings are displaying camera dates two days in the future. It's a bit of a different bug when the DVR sends the date over to the camera since the camera increases it by 2 days. I found a similar result when setting the date via Onvif Device Manager (increases date by 2 after setting it). Setting it internally only increases it by one day...
Regardless, I'm convinced there's a firmware calculation trying to handle February leap year dates and it does it incorrectly. I noticed yesterday that my cameras all showed 3/1/2020 (two days after the real current date). Today they still show 3/1/2020. It doesn't seem to increase the date past March 1st due to this bug. I have a feeling tomorrow they will correctly show 3/1 again, and then start showing the proper current dates on Mar 2nd, 3rd,, etc. until the next Feb in a leap year (2024), since manually setting them to any date in any month besides February in a leap year leaves the date at the set date and does not try to increment it improperly.