Add ¾ cup sugar and ½ cup key lime juice to small saucepan. Turn to low heat and stir constantly until sugar is dissolved. Remove from heat and set aside.
In a medium bowl, sprinkle gelatin packet over 2 tablespoons key lime juice. Stir, then allow to stand 5 minutes.
Add hot mixture to gelatin mixture. Stir until gelatin dissolves.
Whisk in sweetened condensed milk and lime rind.
Place bowl in a larger bowl filled with ice. Whisk until mixture is partially set.
Fold whipped cream into lime mixture. Pour into serving dishes and chill for 8 hours before serving