To make the rosemary syrup, combine sugar, rosemary, and 1 cup water in a small saucepan over medium-high heat; cook until sugar has dissolved, about 3 minutes. Remove from heat and let cool, then strain.
To make the tea, bring hibiscus and 1 cup water to a boil over high heat in a small saucepan; cook 3 minutes, then let cool before straining.
To make the cocktail, combine tea, tequila, syrup, lime juice, and 1⁄2 cup water in a cocktail shaker filled with ice; shake vigorously, then strain into a highball glass filled with ice. Garnish with a rosemary sprig.