You're installing Ubuntu the day after a release, and you've probably checked the boxes to update from the internet, so the installer is downloading updates and language packs.
The main repositories get hammered the day of a release and the following days. The reason your timer is going up and down is because your download speed is varying, and the reason it's taking ages is because the repository is overloaded.
Either start again and don't check the boxes to update components from the internet, or tough it out and wait for it to finish.
If you start again, you can change your software source to a less crowded one using the "Software Sources" tool after installation, and get your updates in the usual manner. There's a wizard that will pick a good repository for you in that tool, or if your ISP offers a mirror (e.g. http://ubuntu.virginmedia.com ) that's probably the best choice.