It took me about half an hour to install the GM on my 16 gig, which included a long backup, but it's still the middle of the night here in CA, so I'm guessing it's not being released within the hour.
This depends on a lot of factors but an hour should be just about enough allowing for slow download and any potential problems.
However if it is anything like when 2.0 came out it could be a long night.
Im not going mental over the update, my phone works fine as it is so I will most likely be installing it tomorrow as Im going over to my sisters tonight.