Is there any reason you can't schedule your full backup as well? It's correct to say that you can backup with users on the system. However, given that your database isn't in full recovery mode, you want to make sure you capture enough transactions to make your full and differential backups as up-to-date as possible. The best way of doing that is by waiting until the working day is over.... assuming, that is, that you have such well-defined periods of activity.

John

Edit: corrected punctuation