When you do a search on eBay for your item, how many are found?
Very common or very rare items, don't think it matters much what day they end. Saturday and Sunday evenings I guess are the most popular, but staying away from others that sell the same thing might bring you a better price.
If your item is somewhere between common and rare, sticking with the evenings, you will have more people on eBay eager to bid as your auction ends, but ending durring the day may draw earlier bids knowing they will be at work the following day.
Not a very clear answer is it?
I end most of mine Saturday or Sunday. Early evening west coast/late evening east coast.