How to Set Up Backup 3 and Save Your Data
Subject:   Backup won't when computer is sleeping
Date:   2005-10-09 11:57:16
From:   AndyBrown
Response to: Backup won't when computer is sleeping

Well... It can be done in theory by setting your computer to wake every night just before your backup is done. You should be able to use the schedule option on the energy saver tab of your System Preferences. But and it's a big but, at least on my system (10.39) this will work once only then reset itself so once again it's back to having annoying messages from Backup when you go back to the computer in the morning.

Ditto above, very frustrating.