Time-dependent hardness of calcium carbonate-polyethylene composites prepared by co-rotating twin screw extrusion has been determined. Hardness of composites were shown to be a power increasing function of the amount of calcium carbonate particles, but decreased as the time under load increased. The degree of time-dependent hardness was observed to be unaffected by filler concentration. All compositions showed similar percentage of hardness decrease with increasing dwell time. A graphical method was devised and able to apply to map the hardness of various filler volume fraction composites at any defined dwell times.