Mine was doing this too and driving me nuts! BUT I fixed it during the upgrade to W10.
I did an inplace upgrade from 8.1 to 10 - worked fine but I lost screen rotation etc as described elsewhere on the forum. That didnt bother me too much as I never use my 10 in any way but landscape. The clock issue really irritated me.
Anyway - to fix it this is what I did (just because this worked for me doesn't mean it will for you and take precautions to back up everything first):
1) Back up Windows 8.1 to USB as described in guides on this forum
2) Upgrade from 8.1 -> 10 . After upgrade W10 was activated and fine and working fine - as mentioned, i didn't have rotation, but wasn't bothered by that.
3) Created a W10 x32 Home (not Pro) USB stick using the MS tool (you can use the method with Rufus etc as described on the forum too)
4) Attached Keyboard, Mouse and USB to USB hub and to Linx10 via adapter cable
5) Completely blew away previous install (as in I deleted all 5 partitions that appeared)
6) let W10 install - as though installing to a new PC
7) after install was completed, installed the W10 drivers (from this forum) - prior to installing those drivers, the touch screen didn't work etc etc, hence needing the USB keyboard and mouse
8) let W10 do any system updates and driver updates
9) clock works!
Its a bit drastic I know, but it worked for me and my Linx10 now has a fraction more space than previously (because I blew away partitions) and it boots just as fast as in the past and everything is now working and working fine.