To make the most out of your Buy It Now listing, start your listing duration at 3-days. Then if no one takes your Buy It Now price, revise your listing to a 5-day listing, and repeat the process if necessary to 7-days and even 10-days if need be. This allows you to make it seem as if your item is always almost ending (your item might sell faster).

I've done this method many times and for me at least, more people will buy your item sooner because people just tend to buy the items that are almost ending rather than the newly listed items. Of course your price should be reasonable as well. In my opinion, this is more effective than just listing your item for 7-days from the beginning. Just remember to revise your auction with more than 12 hours left or else you won't be able to revise it.