I've been having this strange issue with my system clock. Sometimes when I start up Windows 10, my clock displays a time that is 5 hours ahead of the current time. So if it's noon where I live (Eastern time zone), the clock says 5pm. It adjusts for Daylight Savings Time as well staying 5 hours ahead.
I've checked my time zone settings and it's set to the correct time zone. I have internet time set to sync with
time.nist.gov, and when manually synchronizing the time, it correctly sets the clock, although the following error message appears when doing so:
"An error occurred while Windows was synchronizing with time.nist.gov. This operation returned because the timeout period expired."
This issue started immediately after erasing my hard drive and reinstalling Windows 10 from scratch, so it's not caused by anything I've installed since then. It only happens on Windows startup, but not every time. I currently have Ubuntu 16.04 installed in a dual boot configuration (the problem started before I installed Ubuntu), and I haven't seen any similar issues with the Ubuntu clock.
I've looked through similar time-related issues on the internet, but none seemed to match mine. This question is very similar to my own, but the issue there was caused by the hardware clock being off, and the clock shown in BIOS on my computer is set to the correct time.
What strikes me as strange is that the time is exactly five hours off, not a minute more, even adjusting for DST. It would seem to me that Windows is occasionally syncing with the wrong time zone, but I have no idea how to verify or correct that.
UPDATE: It turns out that switching from Ubuntu to Windows triggers the 5 hour offset every time, so it was indeed an issue with the hardware clock being set to Universal/Local by Ubuntu/Windows, respectively.