If you download the DING software, it will automatically update one to three times a day. Each time they will offer fares that are only good for a specific time period- until 8pm, for example. The program "DINGS" when it updates, hence the name. If you are going with southwest, you won't get lower fares than these. You may have to watch it for a few weeks to get the fare you are looking for. If you find a lower Ding fare later, you can rebook and SW will give you a credit which must be used within one year.