Every item has a scheduled closing time. However, if there is active bidding within 5 minutes of the scheduled closing time for an item, that item will remain open until 5 minutes have elapsed with no new bids. Using the refresh button will allow you to see exactly how much time is left before an item will close.
For example:
Equip-Bid's goal is to emulate the live auction process. This practice reduces tactics like bid sniping and ensures that all bidders have a chance to participate in the items that they want.