The best time for an auction to end depends on a number of things:
Popularity of the item - popular items like electronics will tend to have the usual busy periods sunday night.
Target market - If you are aiming to target the market in another country you will need to work out the time difference and list accordingly.
History - The times in the past when your items sold for more are generally the better times.
You also need to know of any big events on in the year and plan around them, e.g Never end items on new years eve, you just won't get a good price.
Hope this Helps!