Working in batches, shake together 1½ cups vodka, ¾ cup Aperol, 2¼ cups pink grapefruit juice, and ½ cup maple (or other) syrup in an ice-filled cocktail shaker. Strain into ice-filled pitcher and stir. To serve, pour into 8 glasses and top each with 3 oz well-chilled tonic water. Garnish each glass with a grapefruit wheel and a sprig of thyme.