In general, you could download your updates with out installing them. Just become root, wait for 2am, and start downloading.
$ sudo bash
# sleep 5h
# apt-get dist-upgrade --download-only
You could create a cron job that executes the last command (especially for regular incremental updates). Then when you wake up, you can install the updates.
do-release-upgrade command (the recommended way to upgrade to the next Ubuntu) doesn't have a download-only option, so I'd stick with ændrük's CD download.
However, if you're feeling really adventurous, you could follow the instructions for setting up commandline upgrade and then run
do-release-upgrade after a sleep. Note: I'd be pretty wary of installing updates when you're not there to see what might go wrong.