Kinetics of porous layer evolution during high-temperature annealing was investigated by Monte Carlo simulation. Sintering process of spongy one-component films with randomly distributed pores was studied. Layers with porosity from 20% to 50% with simple cubic and diamond-like lattices were under examination. Sintering rate was demonstrated to be non-monotone in time for any film porosity and different lattice coordination number. Metastable states of the system, dependent on time and temperature of annealing process, were revealed. Estimation of annealing time necessary to reach the definite sintering level under changes of annealing temperature was suggested.