Binary mixed thin films of picene (C22H14, PIC) and pentacene (C22H14, PEN) consist of crystallites with a statistical occupation of the lattice sites by either PEN or PIC and unit cell parameters continuously changing with the mixing ratio. For high PIC ratios a PIC phase forms which corresponds to a limited intermixing of the two compounds. The growth behavior of these mixtures is investigated in situ and in realtime using grazing incidence X-ray diffraction. We observe a delayed phase separation in PIC-rich blends, i.e. complete intermixing in the monolayer range and the nucleation of a pure PIC-phase in addition to the intermixed phase starting from the second monolayer.