Stress induced changes in intrinsic timescale were investigated by nonlinear creep tests on polycarbonate at room temperature. The creep compliance vs. time curves at nine different stress levels were determined and shifted along the logarithmic time axis to get a master compliance curve at a given reference stress level according to the concept of time–stress equivalence. It is shown that the time–stress superposition principle provides an accelerated test technique for evaluating the material’s long-term mechanical properties.