Good lord, you people are impatient. There has never been a consistent schedule when it comes to releasing the letters other than "approximately twice a month."

I - II: 11 days
II - III: 16 days
III - IV: 11 days
IV - V: 3 days
V - VI: 13 days
VI - VII: 13 days
VII - VIII: 12 days
VIII - IX: 19 days
IX - X: 18 days
X - XI: 21 days as of today...

So as you can see, we've barely passed a few days over the previous longest wait. And given that patch 1.18 is the largest patch thus far, I think a few extra days of preparing for the letter are more than acceptable, especially if we're actually going to get that video Yoshi-P mentioned in his last letter.