For the most part its time based I think its something like 4pm - 2am but they have been known to throttle at other hours then that.But generally yes if you leave it on all night you should be good as it will download faster.
reply to rmk70 A few users have had problems with Bell throttling outside of those hours but for the majority it's just 4pm to 2am. If you're throttled outside those hours talk to Deadpool, he works for Bell.--Taylor Byrneswww.taylorbyrnes.org