The process is intended to be individualized as much as possible, so that one size does not fit all.   That said, the Church in the United States says that an unbaptized adult should be accompanied for at least one full year before they are initiated so that they have a chance to encounter Jesus’ entire story: birth, life, passion, death, resurrection, ascension and coming of the Spirit.  Others need varying lengths of preparation, and the Church intends the process to be adapted according to the needs of each person.