There are two reasons why an item may end after the schedule ending for an auction. First, items in auctions often end is small batches to give bidders a chance to bid on multiple items in the last minute. Most auctions end in groups of 5, however you should check the terms of each auction to make sure you are aware how many items end in each minute.
The second reason is if an item is bid on in the last minute of an auction, the ending time for that item resets at one minute. This makes bidding more exciting and allows all bidders a chance during the final seconds of an auction.