Actually I think the clock stopped when the PC connected to the network - it looks like the 4:09 time is being displayed by a computer which was waiting for connections (I think). In which case the built PC must have booted into *an* OS, although haven't checked whether it's Windoze or not.
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>> I am guessing these guys work in computer factories.
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If you watch the video they have a very detailed instruction sheet, and some of them are looking at it with that look I use when looking at the gearbox dismantling bits of an old Haynes manual.