The functional connection between terms (duration), as chronological modalities of legally relevant activities, and the interests actually pursued by the parties is the cypher to analyse the nature of these elements and their impact on the effectiveness of contracting and on the regulation of relations. And this beyond a conflict between effective and fulfillment dates, in favor of a common unitary function of conforming the structures of legal relations. The objective of the investigation is to requalify terms, from accidental elements, as they are traditionally understood, to functional connotations of contracts, subject to a control of lawfulness and merit. The examination of the application profiles allows us to overcome the narrow perspective of an essential date intended exclusively as a remedy for non-fulfillment, operating on the implementation level of the case, in view of a recovery of the regulatory dimension of interests.