The stability of side-exposed backfill is essential to ensure a successful mining operation. Until now, it has been analyzed without considering the creep of rock mass. In practice, stope excavation and backfilling are always scheduled with different time during which fill mechanical properties can evolve and rocks exhibit more or less creep deformation. In this study, time-dependent stability and minimum required cohesion ( c min ) of side-exposed backfill associated with the creep of surrounding rock mass are, for the first time, analyzed through numerical modeling with FLAC 3D . A distinction is made between the cohesion at failure and c min . Results show that the empty time of primary stope does not significantly affect the stability and c min . When mine depth is small and the rock exhibits little creep, it deserves to wait longer time before adjacent extraction for the backfill to gain more strength. When the mine depth is large or/and the rock exhibits heavy creep, the instability of side-exposed backfill can be dictated by crushing failure. A stronger backfill means also a harder backfill, which absorbs larger compressive stress and is more prone to be crushed. In this condition, a softer backfill can be better through the use of lower binder content or/and with a shorter curing time. The adjacent secondary stope should be filled as soon as possible to avoid failure of side-exposed backfill. More simulations were done on the effects of stope geometry and mechanical properties of backfill and rock mass on the stability and c min of side-exposed backfill. Highlights The empty time of primary stope does not significantly affect the stability of side-exposed backfill. When the mine depth is small and the rock exhibits little creep, it deserves to wait longer time before adjacent extraction for the backfill to gain more strength. When the mine depth is large and the rock exhibits heavy creep, a softer backfill can be better through the use of lower binder content or with a shorter curing time to prevent crushing failure. The extracted secondary stope should be filled as soon as possible to avoid failure of side-exposed backfill. Optimization of sizes for the primary and secondary stopes is needed to minimize the overall backfilling cost.