Any bids placed in the last minute extend the bidding on all the lots in the auction by two minutes. This is to give all bidders the chance to bid again on any lot in the auction.
This means that if an auction is scheduled to end at 4pm and someone places a bid at 3:59pm, the auction is extended by two minutes. The countdown clock is automatically updated to reflect the new auction end time. The auction will keep extending at two minute intervals if bids keep coming in at the last minute of the auction. The auction will end when no bids are placed in the final minute of the auction.