Combine lime zest and juice, lemon zest and juice, sugar, and salt in large liquid measuring cup; cover with plastic wrap and refrigerate until flavors meld, 4 to 24 hours.

Divide 1 cup crushed ice between 4 or 6 margarita or double old-fashioned glasses. Strain juice mixture into 1-quart pitcher or cocktail shaker. Add tequila, Triple Sec, and remaining crushed ice; stir or shake until thoroughly combined and chilled, 20 to 60 seconds. Strain into ice-filled glasses; serve immediately.