Percentage of gfo-like KNe (left) and theoretical KNe (right) following BNS mergers detected by ET in the 2L configuration that are detectable with WST MOS. Different colors indicate different S/Ns; dashed, dotted, and solid lines correspond to the blue, orange, and red arms of the spectrographs, respectively. The highest detectability occurs approximately 12–24 hours post-merger. The peak time of the detectability reflects the optimal observational window across the full range of ejecta masses, compositions, and inclinations considered in our simulations.