Wherever you see an End Date setting throughout the system whether it be in Pricing, Promotions, Item Groups for Item Merchandising, Banner Groups for marketing, Catalogs, Catalog Containers, Products, Blog Post Groups, Brand Groups, Categories etc.. those end dates expire at 00:00:00 UTC time. If you're in the Us in Eastern timezone the expiration time will be the evening prior to the date you set 5 hours pending daylight savings time. Pacific timezone 8 hours. Be sure to take this into consideration when configuring your end dates and troubleshooting issues.