Time resolved photoluminescence in semiconductor microcavities in the strong coupling regime both for non-resonant and resonant excitation is modeled by considering scattering of exciton polaritons by acoustic phonons. Rise time and decay time of the luminescence signal are studied as a function of temperature. The polariton bottleneck effect is put into evidence in model structures which are free of leaky modes. In realistic structures these modes are instead expected to play a dominant role in the relaxation of non-resonant photoluminescence.