You could always make an Automator job that launches SD and then executes an SD backup. Save it as an "application" and use iCal to run the job as often as you want during the day.
Automator/iCal is a great tool that I use all over our network. I find a lot of Mac users have never really paid much attention to the power Automator/iCal provides in automating daily tasks on your Mac. There is literally no limit to what you can do with it.
