When I was allowed to use “after the departing xxx cleared to land” the minima were that at the time the inbound crossed the threshold the departure should be: still on the runway 2500m down the runway or airborne and 2000m down the runway (or could be 1500m if both were props). The scenario described by the Flying Hi sounds quite normal albeit tight except Enter Air at c.300ft is unlikely to have been much less than 600ft in reality.