Here comes the first rumor on the matter. Apparently you should expect rollouts to commence either in late November or in early December. That would be pretty fast for Samsung, even if Google pushes out the new bits tomorrow.
However, there's no release date for Android L to speak of right now. But it looks like Samsung may be working towards having updates ready sooner than usual. This may of course have something to do with the recent moves by some of Samsung's competitors. Last year, HTC and Motorola were both reasonably fast with updates to Android 4.4 KitKat (Motorola far more than HTC).