This maybe too late...
Download Southwest's DING. They are offering flights (little special deals ONLY to DING users, delivered a couple times a day) anytime May 1-May 31. I just bought my sister-in-laws ticket from Tampa to Chicago for $47 each way, $113 total!!!!! And her flight is the 7th, so I did it with only 2 weeks advance purchase. It doesnt matter how short notice. As long as you do it on the days they offer. So, when I did my sisters, it had said Mon-Sun.. But the one I got this morning said Mon, Wed, Sat only... So it just depends.
Also, DING is only helpful if you keep your comp online all day and if you can check it regularly. I stay home, so I hear the ding that chimes off when I get an offer, and I go check it right then.
Good luck!!!