There used to be a ten-year rule but I don't think it is followed as much as in the past:
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km 8/75 p. 6 To All Bodies of Elders ***With regard to one who has been reinstated and who is being considered for further privileges, it is clear that he should have ‘lived down’ the reproach he brought on himself by his wrong act, doing this by building up a convincing record of righteousness that would serve to counterbalance the effect of the past wrong. This might involve only a few years, but possibly many years, to do, depending upon the notorious nature of the wrongdoing. In any case, such reinstated one should first be recommended as a ministerial servant.
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km 12/70 p. 4 Question Box ***If at one time a person had been disfellowshiped or disassociated, may he ever give a public talk? This might occur, but only after at least ten years from reinstatement. (For details see "The Watchtower," 8/15/65, p. 497; "Lamp," p. 121.)
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w65 8/15 p. 497 Turning to Jehovah ***If, because of the blameless conduct of one since his reinstatement, the congregation has come to view him as a good example, then if such a person, who was at one time disfellowshiped but has now returned and shown humility, proved his love for Jehovah’s Word and work for ten years after reinstatement, it would be in harmony with the parable of the prodigal son if such one were used as a congregation book study conductor and allowed to give public talks.
If, since his reinstatement, he has proved himself to be an example to the flock of God during ten years of faithful service, and if the congregation committee sees that such a one can be given a greater privilege of service, why not grant it to him? If he has demonstrated that now he is going to stay in the house of his Father for good, and that he is loyal in his devotion to the interests of that house, it would seem that he could safely be entrusted again with greater responsibility in the congregation of Jehovah’s people.
*** w62 10/15 p. 632 Bible-based Society of Kingdom Witnesses ***
One disfellowshiped and later reinstated cannot be recommended as an overseer or ministerial servant, since his reputation is not above reproach. (2 Cor. 2:5-11; 1 Tim. 3:1, 2, 7; Titus 1:7