Redsniper, since AS queues snipes up about two minutes in advance, I'd say that you couldn't set up a snipe in less than that time. I try to have mine all set at least 5 minutes before auction closing time. So, if you come across something that's closing in less than three or four minutes, I'd suggest you try a manual snipe.
I'd also suggest that you try to snipe with more than 1 second left. You'd miss a lot of auctions that way, especially when eBay's servers are running slow. I use an 8-second interval and that's worked fine for me. After all, it isn't how close to the end you come, it's how much you bid that counts. Sniping is good for avoiding bidding wars, but it's useless if you don't bid enough.