in each auction it will last one day from posting time then the owner will choose the best pokemon and that person will win. now to be more specific.
1. you can create more then one auction
2. you may only place one pokemon in the auction house at a time (no placing two pokemon in the same auction)
3. you may only bid one pokemon at a time ( no bidding two pokemon for one)
4. you can bid on more than one pokemon