Development Release Uploads
Before the final beta freeze of a development release, getting a package into the archive can be done in a matter of hours. You just upload it, when you have tested it and make sure it works locally.
After Final Beta Freeze
After final beta freeze, if a package is included in one of the official flavor ISOs, the package will be stuck in queue for review. (Add more about this here..)
How to upload
Uploading is quite simple. Build the source package, just like you would before uploading to a PPA. Then, just do:
$ dput ../<changes-file>
When using no argument for dput, it will use the Ubuntu archive url by default (on Ubuntu installations only).
About uploading - https://wiki.ubuntu.com/MOTU/New
This does not seem right, though - http://packaging.ubuntu.com/html/udd-uploading.html