Info provided by Nigel Goodwin over on Digital Spy Forum ...
How will Auto Standby work?
Once Auto Standby is activated, customers with Sky+ or Sky HD may see a message pop up on their screen - if there is no activity on their box for two hours (between 11pm and 4am), an on-screen message will be shown saying that their box is about to go into standby. If they are watching TV they need to press 'back up' to continue viewing.
They don't need to worry about any recordings they've set while in standby their box can record up to two programmes at the same time.
When customers turn their box back on, after it has been in Auto Standby, it will be tuned to the last channel they watched.
If customers regularly watch TV in the early hours of the morning it is possible to permanently switch off Auto Standby by using an option in the 'Settings' menu of the Sky Guide. From there they need to go to 'Services', '5 Sky+ Setup', 'Auto-Standby' and then set to 'Off'