It definitely takes some time. I was finally able to download the upgrade after trying three times. After that was the next issue. Many people are getting an error message when trying to upgrade. The notification bar hangs during backing up iPad, then it will extract the data and BAM! Error message 3200 or something like that. Just keep trying and it will eventually upgrade. It took me about 15 times. I was planning on throwing in the towel and waiting until the weekend when the servers wouldn't be so overworked but it just happened to work on my last try
Good luck and keep trying