Magnitude distribution in the Rubini filter (with a cut at m = 30) of afterglows produced by BNS mergers with a viewing angle below 15° (solid black line), at ∼12 hours (top panel) and ∼3 days (bottom panel) post-merger. Dashed- and dot-line black histograms correspond to events that are detectable with WST (i.e. where the combined flux of the afterglow and KN has S/N > 3) and for which the afterglow outshines the KN, for Θ_view < 10° and 10° < Θ_view < 15°, respectively. Dashed- and dot-line gray histograms represent detectable events where the kilonova dominates over the afterglow, for Θ_view < 10° and 10° < Θ_view < 15°, respectively.