§1. Initial probation is to be ordered in a way that the candidates understand more fittingly their own divine vocation, and indeed, the one proper to the institute, and that they are trained in the spirit and way of life of the institute.
§2. Candidates are properly to be formed to lead a life according to the evangelical counsels and are to be taught to transform their whole life into the apostolate, employing those forms of evangelization which better respond to the purpose, spirit, and character of the institute.
§3. The constitutions are to define the manner and length of this probation before first taking on sacred bonds in the institute; the length is not to be less than two years.
Source: Code of Canon Law (Vatican.va)