Well where I am, heavy use between 6pm and 7 am is thereabouts is pushed onto slow lines, so you don't get 8 megabit. I expect 100 KB/s tops on an overnighter, which would take 22 hours for 8 GBs. It's better to download during the day, but of the ISPs don't like people's behaviour, they'll cap it. I think mainstream large downloads will take a couple of days to get realistically on current systems and services, though episodic delivery may hide a lot of that. There'd need to be considerable shake-up of broadband delivery for the majority of users to get complete downloads in a few hours.