The extension would allow for players to finish up current threads and make/plot new threads. Those who have already begun to feel the effects of the Lamba can continue to do so and progress down their path at a rate of the players choosing, so long as they've gone crazy and either been killed or left for the Badlands by the new end date (Dec 7th.)

So, simple answer, it extends both the initial phase and the 'killing machine' phase. (IE a new rough estimate would be 'starts going crazy up to December, is actually crazy during the first week of December'.)