John Gill Commentary Acts 18:11

"And he dwelt [there] a year and six months, teaching the word of God among them." — Acts 18:11 (ASV)

And he continued there
At Corinth, as the Syriac version, and some copies, read; he was obedient to the heavenly vision: in the Greek text it is, "he sat" there, answerable to the Hebrew word (bvy) , which signifies to sit, continue and abide: he stayed there in all a year and six months; which was a long time for the apostle to stay in one place, and longer than he did anywhere, unless at Ephesus, where he continued two years, (Acts 19:10)

for as for his stay at Rome, that was by confinement: but here were many people to be called, and much work to do, a large church to be raised, and put in order; and this required time as well as care and labour:

teaching the word of God among them ;
he did not sit idle here, but preached the Gospel, which is the word of God, and not man, openly and publicly, among them all; and that frequently, in season and out of season, and with great boldness and faithfulness.