The Cordus theory of time suggests that time started when the universe started.
To the level to which Cordus can penetrate, time is a consequence of the frequency oscillations of particules. Its rate is thus determined by the mass of the particule, in turn how it is assembled and from what subcomponents. In that sense even massless particules (photon, neutrino) have frequency and therefore time. However the forward arrow of time arises where coherence lets off and decoherence starts. This discontinuity in the physics of time occurs at different levels of assembly depending on temperature and homogeneity. Time therefore comes from the frequency oscillation of matter, which in turn comes from the primal photon(s) at genesis.
Read more here:
Pons, D.J. (2013) What really is time? A multiple-level ontological theory for time as a property of matter. vixra, 1-40 DOI: http://vixra.org/abs/1301.0074.