If you're using Vegas Pro 8, you can use my Auto Save custom command which will let you specify how much time there is between saves. It will also give you a series of backup files with the date/time appended to the filename as well.
Auto Save is installed when you install Excalibur. It's free and will work perfectly fine with the Excalibur demo even after the demo expires. There were a couple of bad links there, though. These have been fixed.