There is no way that a "normal" backup should run for 30 minutes....unless you are constantly adding new photos, songs, movies, or other heavy data material.
You might want to download and install BackupLoupe, an application that will show you a complete record of exactly what is backed up on each pass.
soma-zone: BackupLoupe
Some applications like Entourage, Aperture, VM Fusion, Parallels and others try to back up their complete database on each pass. In addition to taking up a lot of time, this can fill up a Time Capsule very quickly.
Once you identify the culprit, you can exclude that file or database from backups and back it up manually each day. The goal here is to have your hourly backups take just a minute or two...and not slow down your network.