I started out with week long auctions, then three day. I decided to give the one day auctions a try when they first offered them. The profit margin is about the same and I can sell seven in a week instead of one or two. Sometimes they don't all sell, but generally they do. I list through Auctiva so the cost is almost zero.
I am talking about repetitive merchandise. When I list something such as a vehicle, yes I do list it for three to seven days. However, I am not sure how much is gained. Normally people look at an item when it is newly listed and again during the last day.