You'll just have to keep checking.
And you might need to be flexible, so think of your options before you call. The deal may not have availablility at the resort you already have booked, so you'll want an alternative if you want to take advantage of it.
We've gone in May the last two years.
In 2008, we just got free park hoppers/WP with our tickets.
This year, we got the buy4get3 at Pop Century for part of our stay. They then came out with a spring deal (a certain % off). We were able to stay an additional 4 nights at CSR for $101 a night.
MIL joined us for 3 nights at Pop Century. Shortly before the trip they came out with a FL resident special, so I was able to change her reservation to that deal.