In this paper, I focus on one type of grammatical change consisting of creating periphrastic junctures from nominal sources used in relative clause contexts. This is a periphrase production mechanism that has been increasing the unstable paradigm of junctures and helping delineate Portuguese language grammar. One construction resulting from this mechanism is (na) hora que, in relation to which I propose to investigate form, meaning and history. The central aim is to show the emergence of (na) hora que, a grammaticalization instance in course, in which it is possible to catch stages of the its gradual constitution process, concerning both the syntagmatic reorganization of items with consequent morphological losses, and the constitution of meanings, with the origin of polysemies, pointing to a directionality grounded on the increase of the cognitive complexity.