For best exposure begin your 10 day Auction on Thursday eve at Midnight (EST) to end the 2nd Sunday at 12AM (EST).
Now you have 2 weekends & you give ppl on the West Coast a chance to bid till 9pm California time.
It really depends on the item you are selling
If you are selling an item that isnt a hot item on the market and you need a lot of exposure what you are saying might be true
But if you are selling a hot item - Laptop, tablet, ipod.... or whatever is hot that season... Then too long of an auction isnt good. Because in the beginning of the auction when the price is still low - people bid (prob thinking why not bid low now - this is deff a good price is they win at this bid... Which is really stupid as it jacks up the price...) Either way a few days into the auction the price will get bid up, and now many people arent gonna even look at this item cuz it isnt the low price they wanna get it at....
I have seen that the more watchers on an item the better chance it is for selling high. The item only racks up watchers when the price is still low
I think 3 day auctions are really good.