Just my point of view, but I try and have my coins end on Thurs. nights about 8:30 Eastern time. I live on the east coast, so this seems to work the best for the first two time zones and keeps most shipping a little closer and cheaper. I like Friday and Sat. there after for coins. I have passed this on to CyberDan and believe he agrees with me. I find for vintage collectables the best ending times are the weekend late afternoons to early evenings. I am not an Ebay pro, better info could probably come from Diggummup, but this is my experience. Like I said in an earlier post, I have honestly bought a coins or coins on a Mon. or Tues., maybe even in the morning, gotten it in the mail in a few days, re-listed it or them to end the next Thurs and made money. I can't explain it, but it is the truth. So, my advice isn't to worry about the number of days for your auction, but to schedule your auction to when your target buyers seem to be online shopping.
T.
OH, and P.S. if you do sell coins, the key dates or expensive older ones, with a mint mark that someone might be searching for.............the longer the auction the better, give them time to find it, 7 or 10 days. Also, coins that are worth more in melt than numismatics, like cleaned halves, or holed Peace dollars, list them as 1 day auctions a day when silver spikes. Gets them to the top of the list while the metal is hot. Ok, enough of my opinions for one day. LOL