> I wish to download a large site that may well take
> six or seven overnight downloading sessions to
> complete. I gather that I can cancel and resume from
> where I left off the next night, but can this only
> be done once? 

No idea where you got that wrong idea.

> Can it be done without having to leave my computer
> on and unrebooted for a week?
Press Cancel (ONCE ONLY) and let it finish. 

Once the program stops you can exit, do what ever you like, and Continue on a
later date.