I did the initial pre-patch, while playing a week or so ago, in 30 mins or so for the... what was it 500mb or so?

Today's patch was about 5 mins.

It will vary both by your potential download speed, and how quickly blizzard will give you the data. Or their torrent tracker thing. I average 1mb/sec, when downloading torrents the next day, but rarely hit more then 300k/sec the day my tv show airs.