In a large bowl, whisk together the flour, salt, olives, and instant yeast. Add the water . Mix until the liquid is absorbed and the ingredients form a sticky dough ball. Rub the surface of the dough lightly with olive oil. Cover the bowl with a damp tea towel, cloth bowl cover, or plastic wrap and place in the refrigerator immediately for at least 12 hours. Line a 9×13-inch pan (22.86x32.5 cm) with parchment paper or grease with butter or coat with nonstick cooking spray. Deflate the dough and place it into the pan. Roll the dough ball in the oil to coat it all over. Let the dough ball rest for 3 to 4 hours. Set a rack in the middle of the oven and preheat it to 220°C / 425°F. Sprinkle rosemary over the dough. Pour a tablespoon of oil over the dough. Press straight down to create deep dimples. If necessary, gently stretch the dough as you dimple to allow the dough to fill the pan. Sprinkle with flaky sea salt all over. Transfer the pan to the oven and bake for 25 to 30 minutes, until the underside is golden and crisp. Remove the pan from the oven and transfer the focaccia to a cooling rack. Let it cool for 10 minutes before cutting and serving.