The post-annealing duration dependence of structural and optical properties of polycrystalline β-Ga2O3 thin films fabricated on sapphire (Al2O3) substrate via the spray pyrolysis method are presented. Extending the annealing time for fixed temperature 900 °C from 1 to 2 h improves crystallinity of the films, as evidenced by an increase in the average grain size approximately from 8 to 14 nm, a reduction in the full width at half maximum of the  β-Ga2O3 diffraction peak from 0.43 to 0.29°. However, extending the post-annealing duration to 3 h induces excessive grain coarsening into island-like crystalline domains. These findings demonstrate that for the chosen experimental conditions, a 2-hour annealing at 900 °C represents an optimum for achieving relatively smooth and solid β-Ga2O3 films while balancing crystallinity and film homogeneity.