When did the merienda custom of a light afternoon meal begin in southern Europe, and when did it spread to the Americas and the Philippines?

Wikipedia's Merienda article documents the custom's geography and its name's spread across Spain, Portugal, Italy, the former Yugoslavia, France, Hispanic America, the Philippines, North Africa and Brazil, but gives no year, century or era for when the custom began or for when it reached the colonies. A secondary source (Spanish Sabores) states plainly that the origins of the custom are murky, with no more specific date offered there either.