Pommie5...It most definatley sounds like Tiscali are extending there hours on you...I've heard of the 5pm to 11pm and the 6pm to 12pm peak times....
Do you think you have popped up on their radar as a heavy downloader ??
I think because you can connect without a problem (aside from the times you are stating) that Tiscali are not being very fair with their Fair Use Policy...