7 days is the default listing duration for most sellers and this generally gives plenty of time for lots of buyers to view your listing.
But in some cases a longer or shorter time is better, for example, if you have a really high-demand item, like an iPod, then 3 days can work well. On the other hand, 10 days is worth considering for a big-ticket item like an art-work or a collectible, as potential buyers often need more time to make a decision that involves a significant financial investment.
If you have more items to list why not list the other items in place of those "pretty pictures" you currently have listed. When sales start rolling in then maybe you can re-list the "pretty pictures" (items) again.
Also, I'd like to suggest the Research Labs - it can tell you the ideal start price and listing duration for your product so you have at least a rough idea of how to go about your listing.
Hope this helps :)