That should be in your contract with the Auctioneer. It is negotiable, but many Auctioneers have standard policies regarding Move Out dates. I've seen, "Be out 1 Week Before" & "You have 1 Week to Get Out". They should tell you this type of info in the first contact. I also recommend interviewing several Auctioneer services! Don't use the first one you come to! The good ones will WORK for your business.
Selling your home at Auction in a down market is tough to do. Everyone is looking for BIG DEALS so don't expect to make anything off of the home.
Because of "the Market", you might through in a few Realtors in the interview process as well. I'd love to be able to help you. Let me know if there is anything I can do.
Here are some good Resources:
Tips for selling your home at Auction: http://homes.wsj.com/columnists/housetalk/20060807-fletcher.html
National Auctioneers Association: http://www.auctioneers.org/