From the Q3 CC: "We expect to achieve a production rate of 5,000 Model 3 vehicles per week by late Q1 2018, so probably sometime in March...I'd like to state a number at the end of Q4, but there's too much uncertainty right now to give that with any precision. Now I do feel confident about the end of Q1, maybe sooner.
I'm still confident these are achievable projections rather than aspirational, so I'm guessing March.