Cerium-doped lanthanum bromide (LaBr3:Ce) is a scintillator that presents very good energy and timing resolutions and it is a perfect candidate for photon detector in future experiments to search for lepton flavor violation as in mu arrow right e gamma mu arrow right e gamma or mu arrow right e mu arrow right e conversion. While energy resolution was thoroughly investigated, timing resolution at several MeV presents some experimental challenge. We measured the timing resolution of a 3 in.3 in. cylindrical LaBr3(Ce) crystal versus few reference detectors by means of a nuclear reaction from a Cockcroft-Walton accelerator that produces coincident gamma gamma -rays in the 4.4-11.6 MeV range. Preliminary results allow us to extrapolate the properties of a segmented gamma gamma -ray detector in the 50-100 MeV range.