Brownies from a mix are typically baked in a standard sheet pan. When baking them in cupcake or muffin tins, keep the oven temperature the same but alter the cooking time slightly. Keep in mind that the size of the cupcake tins and the amount of batter in each cup influences the baking time.
Use the same baking temperature recommended on the box for a 13x9x2 pan, which is usually 325 or 350 degrees Fahrenheit. For mini-cupcake tins, the cooking time typically remains the same as what is recommended for the 13x9x2 pan, while standard cupcake tins need two to three additional minutes in the oven.
Your Own Style
Fill cupcake tins only half full, as the volume makes a difference in how quickly the cupcake brownies cook. In general, brownies baked in standard-size cupcake tins take from 20 to 30 minutes, with variations for whether you like moist, chewy or cake-style brownies. Follow recommended baking times on the box, but adjust according to your preferred style.