I was downloading a 500 mb update the other day for a game, and the time was originally 3 minutes, by the time it got to 50% done it said it had 9.8 hours left.,(reply>), Many ISPs have burst downloading, you get a very high download rate for say 30 seconds which is great for loading web pages but the sustained download rate is lower. The initial estimate was based on the burst download rate which is faster than the overall average.