I just pulled my Consumer Reports Mag....It states most airlines post their fares for the coming weekend between Monday & Wednesday....
For last minute deals go to:
http://www.airfarewatchdog.com/
the employees comb airlines for significant airfare changes, then post them immediately, sometimes hours before they filter through to large computerized search sites.
Airlines typically change domestic airfares at 10a.m., 12:30 p.m. , & 8 p.m. on weekdays...& once a day on weekends at 5 p.m. Some of those fares only last a few hours...this is according to airfarewatchdog.....
http://www.site59.com/
This site specializes in short trips for the upcoming weekend & the following one....domestic flights between Thursday & Saturday can be booked two weeks or as little as 3 hrs ahead of flight...the catch is all sales are final , so be sure before you book
http://www.kayak.com/
This site scans hundreds of sites for the best deals...beware some fares can change in the middle of booking, which can happen at any site....