If you are a Disney Visa holder, they usually get 3 days advance notice/booking window. It will also be on the WDW website under special offers.
But, I ALWAYS see it here on the code board first!!
There is a code right now for August into September...
The Fall codes should get released sometime next month (start watching the 10th or so of the month) and should cover parts of October, November and December (with most holidays being blacked out)
I believe in the past, the discount for January and February have been free upgrade to park hoppers and water park passes, not necessarily room discounts.