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.
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