Your goal is to maximize the closing price for the item you are selling on eBay. How can this be accomplished? In most cases the majority of bidding activity takes place within the final hours of the auction, sometimes within the last few minutes or seconds. The more bidders that have access to an auction, the more competitive the bidding will be, which will drive the closing price of the auction up. So, the best time to close an auction on eBay is a time where the highest possible number of bidders have access to bid on the item.
You will find different items, depending on the nature of the item, will have different ideal closing times. For example, if you are selling an item for kids, the parents who are the ones bidding on the item will probably have access either during the daytime when the kids are at school or napping, or in the late evening after the kids are in bed. While I can't recommend one single best time for all items, my experience over the last 7 years has led some observations below.
Most people surf the net in the evenings when they get home from the office, so closing times during evenings between 6-8 P.M. PST (9-11 P.M. EST) seem to be ideal times for auctions with consumer goods.
People are typically occupied during Friday evenings and Saturdays, so these times are probably not the best for an auction to close.
In some cases Sunday evenings between 4-6 P.M. PST (7-9 P.M. EST) prove to be good times for an auction to close since most people are at home in preparation for the start of the next week.
During the week, Tuesdays through Thursdays seem to be ideal days for items to close, mainly during the evenings. Thursday evenings in particular seems to be a really great time for auctions to close.
If you have a specialty item, you might consider accessing historical data on eBay, identifying the average closing price for a particular item. With this information, you can sort by price and identify what closing time the highest priced items sold at. Use this information as a guide to the best closing time for your particular item.