  In this work we investigate creep flow of aqueous suspension of Laponite, a
model soft glassy material, at different aging times and stresses. We observe
that this system shows time - aging time - stress superposition over a range of
aging times and stresses when real time scale is transformed into effective
time scale. Existence of superposition in an effective time domain facilitates
prediction of long and very short time rheological behavior. Analysis of the
observed behavior from effective time approach suggests that superposition is
possible only when the shape of a relaxation time spectrum is preserved at
various aging times and stresses. We also observe that creep curves at low
aging times and greater stresses demonstrate delayed but sudden yielding. The
critical time, at which material yields, increases with increase in aging time
and decrease in stress. We argue that local rejuvenation of part of the glassy
material causes variation in the rate of evolution of relaxation modes. The
resulting interplay between aging and rejuvenating modes lead to delayed
yielding as observed experimentally.
