So we can only guess. And the only information we have is breadcrumbs in the developer logs. In September, he wrote that he had reached the 2,000 renders milestone. He also wrote that he estimated the full length of Chapter 4 at 3,000-3,500 renders. (Fun fact, in April, he estimated the total at 2,500-2,800 renders.)
In a recent devlog, in the next episode of the Tax/Workstation saga, he wrote that his current hardware allows him to do 25-40 renders per night. Not sure what this mean - he doesn't do the rendering at the days? I take it as the throughput per day.
So, given that there are 3500-2000 = 1500 renders left, and that he's doing 25 (pessimistic estimate) renders per day, it'll take 60 days just to render that amount. But he has animations planned, and he's going to do them after the static renders are done, in postwork phase. So a very optimistic estimate is ~2.5 - 3 months to complete.
But! It is not clear from the log, these 25-40 renders per day - are these renders only WiAB or WiAB + SG?
If it's the latter, then you can safely multiply my estimate by 2 or even 2.5, since he usually prioritizes SG over WiAB.