Put saffron and 1⁄2 cup boiling water into a small bowl and let steep for 2 hours.
Dissolve yeast and 1 teaspoon of the sugar in the warm milk in a small bowl; set aside to let rest until yeast is very frothy, about 20 minutes.
Meanwhile, put flour, salt, and margarine into a large bowl and rub together with your fingertips until mixture resembles coarse meal. Make a well in the middle of the flour mixture and add saffron with its liquid, yeast mixture, remaining sugar, and dried fruit. Mix with your hands until dough is smooth and comes away from sides of bowl easily, about 1 minute. Transfer dough to a lightly floured surface and knead briefly until dough comes together into a neat ball. Wrap dough in a slightly damp tea towel and place in a large bowl. Wrap bowl with a blanket or a thick towel and set aside in a warm spot to let rise until dough doubles in size, about 8 hours or overnight.
Unwrap dough, scraping off any dough that sticks to the towel, adding it back to ball of dough. Transfer dough to a lightly floured surface and knead for 5 minutes. Divide dough into 18 equal pieces and, using your hands, roll each into a ball. Place balls, well spaced apart, on 2 baking sheets, cover with plastic wrap, and set aside in a warm spot to let rise, about 1 1⁄2 hours.
Preheat oven to 350°. Remove and discard plastic wrap. Bake buns until golden brown on top, about 30 minutes. Serve while still hot or transfer to a wire rack to let cool completely. Store buns in an airtight container for 3 to 7 days and eat, toasted, with butter, if you like.