A seller can end an auction listing early to sell to the then highest bidder at the then "current bid" at any time. S/he can end early without a winner with some restrictions and fees.
If you mean you tried to submit a bid with a few seconds left on the countdown, the countdown is slow because it doesn't take into account latency between you and eBay. Your bid must be received at eBay's servers before the end of the last second.
