Realism's own Wikipedia treatment gives a start year (1848) but names no end date. It describes Naturalism as having emerged from Realism's later phase and heralded the arrival of Impressionism, a gradual transition rather than a clean break, and Realism's own entity-description already records that it directly prepared the ground for Impressionism.
What would resolve this A source naming a specific year or event as Realism's own close, rather than only describing its gradual dissolution into Naturalism and Impressionism, would resolve this; current art-historiography treats the boundary as porous.
OpenWikipedia