Acts 15:36

‘And after some days Paul said to Barnabas, “Let us return now and visit the brethren in every city in which we proclaimed the word of the Lord, and see how they fare.” '

After some days' is vague and allows for a considerable amount of time. But eventually Paul suggests to Barnabas a round trip in which they will visit all the cities where they had proclaimed the word of the Lord, in order to ensure that the churches were prospering, and no doubt with a view to ministering to them.