I have the same problem with HP Envy X2 on Windows 8.1. The system clock is several hours/days ahead when Windows starts up. It doesn't happen every time, but occasionally.
All updates are installed, BIOS settings are fine, Windows Time service is set to launch automatically.
It happens on a clean install of Windows 8.1, even without any OEM drivers.
It doesn't happen on Windows 8, so this is clearly a 8.1 issue. It seems to affect a lot of Clover Trail tablets, which are all on the same platform.
Please fix this.
Also, forgot to add: Turning off Fast Startup doesn't help. The clock is also messed up when resuming from hibernate.