[Kwpolska]

> Sometimes my cellphones randomly have a wildly wrong time -- a misbehaving (or malicious) cell-tower perhaps?

If you experience that often, I would probably disable the setting to automatically set time from the network.

> booting between Windows and Linux screwing up the system timezone setting

That’s easily fixable with one registry change (RealTimeIsUniversal). You can also tell Linux to use the local time, but Linux will be less happy about that than Windows (Linux won’t write to the real-time clock automatically, for example).