Not all your downloads... But if you move a lot of traffic outside those hours you will start losing stars. On a 2meg account I guess you'd be safe until you average more than 2GB a day for 10 days. Wild guess though so don't take my word for it.
It is a bit weird that their business accounts work optimally between 12 and 6. Guess they are the preferred ISP for Teazers and massage parlours.