The formation of two-dimensional (2D)-hexagonal (p6m) silica-based hybrid material with a dual-mesoporosity is investigated in situ using synchrotron time-resolved Small Angle X-ray Scattering (SAXS). The material is synthesized from a mixed micellar solution of a nonionic fluorinated surfactant, RF₈(EO)₉, and a nonionic triblock copolymer, P123. Both mesoporosities, with pores dimensions at 3.3 and 8.5 nm respectively, are seen by Nitrogen sorption, TEM and SAXS. The in situ SAXS experiments reveal a mesophase formation in two steps. First the nucleation and growth of a primary 2D-hexagonal network (N1) associated to mixed micelles containing P123, then followed by the formation of the second network (N2) associated to micelles of pure RF₈(EO)₉. The data obtained from SAXS and TEM suggest that N1 is used as nucleation centers for the formation of N2, that would result in the formation of a grain with both mesoporosities. Understanding the formation mechanism of such material is an important step towards the synthesis of more complex materials with a fine tuning of the porosity.