  Detecting post-merger features of merger remnants is highly dependent on the
depth of observation images. However, it has been poorly discussed how long the
post-merger features are visible under different observational conditions. We
investigate a merger-feature time useful for understanding the morphological
transformation of galaxy mergers via numerical simulations. We use
N-body/hydrodynamic simulations, including gas cooling, star formation, and
supernova feedback. We run a set of simulations with various initial orbital
configurations and with progenitor galaxies having different morphological
properties mainly for equal-mass mergers. As reference models, we ran
additional simulations for non-equal mass mergers and mergers in a large halo
potential. Mock images using the SDSS $r$ band are synthesized to estimate a
merger-feature times and compare it between the merger simulations. The mock
images suggest that the post-merger features involve a small fraction of stars,
and the merger-feature time depends on galaxy interactions. In an isolated
environment, the merger-feature time is, on average, $\sim$ 2 times the final
coalescence time for a shallow surface bright limit of 25 mag/arcsec^2. For a
deeper surface brightness limit of 28 mag/arcsec^2, however, the merger-feature
time is a factor of two longer, which is why the detection of post-merger
features using shallow surveys has been difficult. Tidal force of a cluster
potential is effective in stripping post-merger features out and reduces the
merger-feature time.
