Evidence that the council was after Paul's first trip to Macedonia
Knox's first argument: Paul's eagerness to "remember the poor"
Gal 2:10 reads "They asked only one thing, that we remember the poor, which was actually what I was eager to do." This request to "remember the poor" is dated to 48 or 49 AD and Paul's collection of money for Judea was delivered in 56 or 57 AD. This interval of 8 years seems too long, especially given Paul's eagerness. Why would Paul wait such a long time to respond to the request. If the conventional sequence of events were correct then Paul's Galatian readers would surely have retorted, "Well if you were eager, why did you wait so long instead of collecting money from us immediately after the request was made?". Knox's solution to this problem is, of course, to place Paul's Jerusalem visit of Gal 2:1-10 after his stay in Corinth, and this means that the delivery of the collection would be 3 or 4 years after the request was made.
However, Knox is too quick to assume that the collection from the churches of Achaia and Macedonia was Paul's first such collection after the request to "remember the poor". He defends this assumption by stating that there is no evidence of any other collection in the intervening years (1987 p38-39). But there are 3 independent pieces of evidence that suggest that Paul collected funds from Galatia soon after the request was made.
1) 1 Cor 16:1-3 mentions a collection from Galatia. It is unlikely that this was to be delivered at the same time as the collection from Corinth, since Galatia is conspicuously absent from the donor provinces that Paul mentions in Rom 15:26.
2) Larry Hurtado has shown that Gal 2:10 itself suggests that Paul had asked the Galatians to give money to the poor in Judea (and that the agitators had taken this to mean that Paul was obedient to the Jerusalem apostles, which is a charge that Paul denies by saying that he had been eager even before he was asked). See my earlier blog post, here. Now, Paul does not encourage the Galatians to collect money in his letter and there is no indication that the collection is still on-going. It is therefore likely that the collection, to which Gal 2:10 refers, had been completed before the letter was written.
3) Titus was in Jerusalem with Paul (Gal 2:1-2) so he knew the needs of the poor in the church there. Titus was therefore Paul's obvious choice to go to (south) Galatia to organize a collection. The collection from Galatia therefore explains why Timothy (who's first name was Titus) was already in Galatia when Paul arrived (Acts 16:1-3) a few months after the conference. Paul had sent him there to arrange a collection.
It seems to me that these three arguments, in combination, show that Knox was wrong to assume that Paul made only one collection after being asked to "remember the poor". While Knox reduces the time interval from 8 years to "3 or 4 years", he is not able to reduce it any further. If 3 or 4 years is better than 8 years, then the interval of a few months, determined by my proposal, is even better.
Knox's second argument: The brevity of Acts 18:22
Knox (p49) drew our attention to Acts 18:22 where we are told simply that Paul landed at Caesarea and then "went up", presumably to Jerusalem. Luke's account of this visit is strangely brief, which supports Knox's view that Luke has taken the events of this visit and brought them forward to Acts 15. However, Luke is equally brief about Paul's visits to Antioch, Galatia and Phrygia in these same verses (Acts 18:22-23). What advantage is an explanation for Luke's brevity concerning Jerusalem if it does not also explain his brevity concerning these other places? And is the brevity really so strange? I have argued before that Acts was written for the Aegean churches. Luke focusses on a) the history of how the faith found its way to the Aegean churches, and b) events where he was personally present (which included not only the "we passages"). Paul's tour in Acts 18:22-23 belongs to neither category so we should not be surprised that Luke gives few details.
The Knoxians' third argument: "The beginning of the gospel"
Phil 4:15-16 reads
You Philippians indeed know that in the early days of the gospel (The Acts chronology places Paul's evangelization of Macedonia some 15 years after his conversion, which can hardly be described as the beginning of the gospel for him. Knox places Paul in Macedonia only 6 years after his conversion, and feels that this explains how Paul can write that he left Macedonia "in the beginning of the gospel". I, along with most commentators, think Knox misunderstood Paul's time reference here. The time interval between Paul's conversion and the Philippians' acts of benefaction is not relevant to the context. Paul is here praising the Philippians for being so generous even in the early days of their faith. It was the beginning of the gospel for them. It is interesting to note that Paul never asked any province to contribute funds for Jerusalem until a few years after their evangelization. For the Philippians to give to Paul so soon after their conversion went beyond the call of duty and Paul praises them for that. This understanding of Phil 4:15 is confirmed by verse 16, where he accentuates the same point about the Philippians displaying generosity so soon after their conversion: "For even when I was in Thessalonica....". , when I left Macedonia no church shared with me in the matter of giving and receiving, except you alone. For even when I was in Thessalonica, you sent me help for my needs more than once.
Arguments for placing the council before Paul's first trip to Macedonia
The Acts narrative is demonstrably correct about the sequence of Paul's journeys, especially in the relevant time period. Luke was a participant in many of the events, as were many in the Aegean churches, to which he wrote. They would not have been ignorant of the correct sequence of events.
It is impossible to cut Acts 15 from its context and paste it into Acts 18:22 without doing violence to one or both passages. Knoxians seem quite evasive on the question of exactly which events of Acts 15:1-16:5 they wish to move to after the evangelization of Macedonia. In Acts 15 Paul travels to Jerusalem from Antioch and is accompanied by Barnabas. In Acts 18:22, however, he travels from Corinth via Ephesus and Caesarea, and Barnabas is nowhere in sight. Indeed, Paul had already split from Barnabas over John-Mark, and Paul's split from Barnabas is the occasion for Paul's selection of Silas-Silvanus (Acts 15:39-40), who was definitely with Paul during the evangelization of Macedonia and Corinth. Furthermore the conference of Acts 15 is a past event by the time of Acts 16:4. The circumcision of Timothy in Acts 16:3 must belong before the second missionary journey: why would Timothy need to be circumcised in time for the 3rd missionary journey but not for the second? Paul's Jerusalem visit of Acts 15 is simply too intertwined with its context to be a duplicate of a visit glossed over at 18:22.
Gal 2:2 reads "Then I laid before them (though only in a private meeting with the acknowledged leaders) the gospel that I proclaim among the Gentiles, in order to make sure that I was not running, or had not run, in vain." It seems that Paul needed the endorsement of the Jerusalem church leaders. Now, he would have needed this endorsement before his "second missionary journey", which was a mission the he led. Knox must explain why Paul would manage without any endorsement during his "second missionary journey, but then require that endorsement before his "third".
For me, a strong argument against the Knox chronology is that it places the events of Gal 2:1-10 after the text was written! I see Paul's letter to the Galatians as Paul's response to the confusion that resulted from his circumcision of Timothy (see Gal 5:11 for example). Paul would surely have cleared up that confusion when he passed through Galatia (Acts 18:23), so the letter belongs to the second missionary journey, not the third.
The Acts chronology is confirmed by the Gallio inscription, which places Paul's first visit to Corinth in ~51AD. Knox and, especially, Lüdemann hypothesize that Luke may be correct that Paul was brought before Gallio, but that it may have happened during a later visit by Paul to Corinth. This is a desperate move. Acts 18 is a unity rather than a conflation of events from two different visits. Sosthenes (Acts 18:17) was Crispus (Acts 18:8) renamed, and he had left Corinth by the time that 1 Cor 1:1 was written.
In conclusion, the Knox chronology has nothing to recommend it. Luke, even though he probably did not read Paul's letters, has written a better "Letters-based" chronology than Knox was able to do.