Cross reference
Acts 18:11
11 And he was there for a year and six months, teaching the word of God among them.
Acts 14:3
3 So they kept there for a long time, taking heart in the Lord, who gave witness to the word of his grace by causing signs and wonders to be done by their hands.
Acts 19:10
10 And this went on for two years, so that all those who were living in Asia had knowledge of the word of the Lord, Greeks as well as Jews.
Acts 20:31
31 So keep watch, having in mind that for three years without resting I was teaching every one of you, day and night, with weeping.