tlcmd: The Ubuntu document, although slightly old, entitled "UbuntuTime
" may explain what is happening. See...
Multiple Boot Systems Time Conflicts
Operating systems store and retrieve the time in the hardware clock located on your motherboard so that it can keep track of the time even when the system does not have power. Most operating systems (Linux/Unix/Mac) store the time on the hardware clock as UTC by default, though some systems (notably Microsoft Windows) store the time on the hardware clock as the 'local' time. This causes problems in a dual boot system if both systems view the hardware clock differently.
You need to decide whether your PC's hardware clock should use UTC or
local time, and then configure both