Periodic Shadowing:
This feature allows you to specify a time delay from 0 to 60 minutes between shadow runs.
This is particularly useful if you use your notebook at irregular times each day.  If you specify a delay of 0 then shadowing will be continuous and (almost) instantaneous providing the most responsive co-ordination and backup strategy. 
 
A note about screen savers:
If you specify a delay of 0 then you may find that your screen saver stops working. This is because Notebook Shadow is continually checking for changes to the files on disk and the screen saver program interprets this as "activity" and does not allow the screen saver to cut in. If you select a delay of 1 minute or more you will find that the screen saver will work OK.