Bring port, brown sugar, and vinegar to a boil in a heavy saucepan over medium-high heat, stirring until sugar dissolves. Add cranberries, cherries, and five-spice powder. Simmer uncovered, stirring occasionally, until cranberries have popped and relish is reduced to about 1 cup, 10 to 15 minutes.
Preheat oven to 400°. If your ciabatta loaf is thick, slice off top 1/2 in. or so and trim sides. Save top and side trimmings for another use, such as bread crumbs.
Slice loaf in half lengthwise, then cut into rectangles about 2 in. by 3 in. Brush cut sides with oil, put on a baking sheet, and bake until pale golden, about 10 minutes.
Sprinkle goat cheese log with thyme and serve with toasts and cranberry relish.