§1. When the time limits mentioned in cann. 1659 and 1660 have elapsed, the judge, after an examination of the acts, is to determine the formula of the doubt. Next, the judge is to cite all those who must take part to a hearing which must be held within thirty days; the formula of the doubt is to be attached to the citation of the parties.
§2. In the citation the parties are to be informed that they can present a brief written statement to the tribunal to verify their claims at least three days before the hearing.
Source: Code of Canon Law (Vatican.va)