If you place a bid when there is less than 1 minute left of the auction, the auction will automatically be extended by 3 minutes. This is intended to give other bidders a chance to counter.
This 1 minute limit applies to the time when Auctionet receives a bid. Depending on your Internet connection, the countdown you see may deviate from this time by a few seconds.
Example:
The auction ends at 10:10:00.
You place a bid at 09:58:30, with slightly more than a minute to go. There is no extension.
You place a bid at 09:59:30, with less than a minute to go. The auction is extended by 3 minutes. The new ending time becomes 10:02:30.
The same auction can be extended more than once, if it receives a last minute bid each time.
Auctions can exceptionally be extended by 24 hours due to technical issues. Read more about that.
During and open absentee bidding before a hammer auction the bidding will not be extended. The absentee bidding closes on a pre-defined time which is usually when the hammer auction begins.
Read more How do I place bids on a hammer auction?