If you cannot guarantee that your computer will be powered on and awake at your scheduled backup time, you should consider downloading and installing Anacron.
Anacron will ensure that your backups are performed as closely as possible to the appropriate daily, weekly or monthly intervals, regardless of when your computer is actually on. It will periodically check for overdue backups and perform them as necessary. (This is very useful for laptop owners.)
If this sounds interesting to you, you can find out more about (and download) Anacron here:
Anacron for Panther
Anacron for Tiger/Leopard
If you have installed Anacron and wish to begin using it with Deja Vu, quit System Preferences and enter this command in a Terminal window:
defaults write com.propaganda.DejaVuPref UseAnacron -bool true
Then open and quit Deja Vu. After you have done this, the popup menus in your Options -> Schedules tab will be disabled. This is because you have decided to allow Anacron to choose appropriate times based on the computer's availability.
To stop using Anacron with Deja Vu and revert to the default scheduling system, perform the same steps, only enter this command instead:
defaults write com.propaganda.DejaVuPref UseAnacron -bool false