eBay Stores is changing the duration options available for Store Inventory listings in the next few weeks. Right now, sellers can choose to have Store Inventory listings run for a several different lengths of time (ranging from 30 to 120 days), or run until cancelled. eBay said because very few Store sellers decide to have their listings run for 60, 90, or 120 days, it will remove those duration options.

Any Store Inventory listings running with one of these durations will not be affected, but once the change is made, sellers will not be able to list new items, or re-list closed items, at those durations. Sellers may still opt to run listings for 30 days, or keep them as "Good 'Til Cancelled."

http://www2.ebay.com/aw/core/200601121422182.html