Most bidding occurs in the last couple hours of an auction.
For items that are common, many people won't even bother to look at auctions that have days or even a week left to go. Rather they'll click on the ones that are ending soon. That way they may get the immediate gratification of finding the item they want and winning it on the same night, and they also can have a clearer idea of the likely ending price before getting emotionally involved. Hence the auctions that end on the day of the week and at the time of day when most customers are connected will get the best results. The two top auction sites, eBay and Amazon, don't give you a choice of when your auction will end.