The time-dependent reliability of material properties significantly affects the long-term reliability of masonry, limiting the accuracy of traditional static reliability analysis methods in evaluating performance evolution. This study investigated axially compressed reinforced concrete block masonry to address long-term service degradation. The Probability Density Evolution Method (PDEM), combined with the number-theoretic point selection method and Total Variation Diminishing (TVD) finite difference scheme, enabled efficient numerical solutions. Sensitivity analysis systematically examined how equivalent cover depth and reinforcement diameter affect time-dependent reliability. Results indicated that increasing the equivalent cover depth from 24.7 mm to 34.7 mm with constant reinforcement diameter significantly delayed corrosion initiation, thus postponing reliability decline. With constant cover depth, increasing reinforcement diameter from 12 mm to 18 mm effectively slowed reliability degradation by enhancing initial load capacity and providing greater sectional redundancy, maintaining the reliability index above the target threshold. Comprehensive analysis demonstrates that increasing reinforcement diameter offers superior life-cycle reliability benefits compared to increasing cover thickness. Comparison with 1,000,000 Monte Carlo Simulations (MCS) validated the method's accuracy and efficiency.