What are we talking about?
Is this for all green card applicants?
No, this concerns only applicants for U.S. family-based green cards who are not immediate relatives, and who were not born in (or chargeable to) Mexico or the Philippines (and India for F4).
What does the visa bulletin say?
For the month of December 2017, and for all countries except the Philippines and Mexico:
Can adjustment of status applicants use filing dates to file the I-485?
Yes, for the months of November 2017 and December 2017, they can. The “gain”, that is to say how many days earlier than the final action date the applicant can file the I-485 is indicated. For the month of December 2017, and for all countries except the Philippines and Mexico, the filing dates are as follows:
The final action dates advances three weeks to August 15th, 2005. We could have hoped for a bit of a stronger start of the year, but it does look like we are going to have to settle for a 3 or 4 weeks advancement each month for the foreseeable future.