I called southwest when I was waiting for them to open up for January 21st. Well, I called and they were able to tell me when they opened those dates last year.
Well, they were off by about 1 week (they came out one week later)
I also asked if they would come out on a Tuesday, because that is the day they have all their new specials, and she said that there is not rhyme or reason to when and what time they come out, but to keep checking, possibly a few times a day.
Just an FYI, I booked our flights a few weeks ago, and got the lowest fair they offer for the flights, and even though the flights are still open, the "lowest" rate has gone up $5 each way. I don't know why. Perhaps because they just opened a whole new section at our local airport and they are subsidizing it.
Good Luck!