Add blueberries, lemon zest, lemon juice, balsamic vinegar, maple syrup, thyme leaves, and ¼ teaspoon salt to a medium pot. Simmer over medium to medium-high heat for 8-10 minutes, stirring often, until thick and jammy but still a little runny. It'll continue to thicken as it cools. Option to mash any berries that haven't popped. Season to taste.