We present results of the investigation of spectrally resolved photoluminescence decay in porous silicon on the time interval which spans seven orders of magnitude. The luminescence decay can be interpreted in terms of a fast bimolecular recombination of free carriers in the core of silicon nanocrystallites and of a slow recombination of localized carriers in the surface states. The etching time of the samples has an effect on the relative weight of both components and on the dynamics of the slow recombination. We discuss the dependence of relevant parameters on the etching time of the samples.