El Calafate is not the attraction. It's a wind-blown town of about 23,000 people on the south shore of Lago Argentino, named after a bush with dark-blue berries, and it exists because of what lies 80 km to the west: Los Glaciares National Park, a UNESCO World Heritage Site since 1981, fed by an ice cap that is the largest outside Antarctica, Greenland and Iceland. Its star, the Perito Moreno glacier, is a wall of ice about 5 km wide that you can watch from a few hundred meters away while it cracks and drops pieces into the lake.
Three days is the right length because the glaciers need two full days and the weather needs a spare one. Patagonian wind is not a detail here: summers are mild but windy, frost is possible even in midsummer, and a day of low cloud can flatten a view that took you hours to reach. Three days gives you one glacier day on the road, one on the water, and a flexible day in town that you can swap with either when the forecast says so. A fourth or fifth day only pays off if you're heading to El Chaltén or Chile.
The plan: day one is the town, the lake shore reserve and the Glaciarium, day two is Perito Moreno, either walkways and a short boat ride or a full day on the ice, and day three is the long boat day to the Upsala and Spegazzini glaciers (with a ranch day as the calm alternative). Start on any weekday, since the glacier and the boats run daily in season, but book the ice and boat trips first and then shuffle the town day around the forecast. If you're continuing north, El Chaltén is a three-hour bus away, and the rest of the country is on the Argentina page.