I think it is on at 12.30am i.e. 30 minutes after midnight on Saturday so technically very early on Sunday Morning. I just stick a 4 hour blank video in the VCR at bedtime and press record.
The only problem is if your STB goes down in which case you may not record it. Make sure the 'now and next' bar is not showing on the screen as the VCR will record that too!! Might be worth doing a reboot before you start recording just to clear any glitches out of the system.
It's a bit of a pain Sky doing this change particularly as many people won't swap to Sky because they don't offer broadband.