Melt butter in a large skillet over medium heat. Stir in the blueberries, blackberries, 1/4 cup sugar, and 1 tbsp lemon juice. Cook until the juices release from the fruit, up to 4 minutes or so.
Stir in the thyme, black raspberries and red raspberries. Add the remaining sugar and additional lemon juice to taste. All of this will depend on the sweetness of the berries.
Serve warm over crepes, pound cake or on ice cream.