Today is my first day trying this out! A couple of items don't close for three days--if I am overbid before the end of the auction, can I amend my 5 second bid? THANKS!!
LL

Sure, if you get to it in time. You can always modify your bid and/or the time it's entered by AS; there's a little icon "Modify Bid" you can click on to do that.

I get sent emails from AS warning me that my snipe amount is below the current highest bid on Ebay. I don't know how often AS check the lined-up snipes to the current bids - perhaps they could tell us?

Obviously this fine when there is plenty of time to correct your snipe. Sometimes you don't get the chance but that is just a risk of sniping I guess.