It is probably because of the postcode you used for Guided Setup on each TiVo. If postcode is between 5100 and 5999 then that would definitely explain the time difference - you should see clock 30 minutes fast and tv guide 30 minutes fast.
If that is it (or you're not sure) then I suggest doing Guided Setup again and make sure you use postcode 5000 (for anywhere in South Australia).
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