Most of the time in the past, say, two years or so, you could count on the hours being released around the 10th of the month two months prior, which would put your target date at August 10th. However, the past few months they've not held true to that formula. Sometimes they come out early, sometimes they come out late.
You could see them any day, but you may not see them until mid-August. I say do what I did for August Park Hours - check every single day, in the morning and at night. And check the DISBoards too, because someone may hear something before the official site actually posts the hours (the CM's on the WDW phone line can sometimes give them to you before the website catches up)
Good luck, and happy planning!
Jon