Place lemonade jelly crystals in a heatproof jug. Pour over 500ml (2 cups) of the boiling water and stir until jelly dissolves. Transfer to a small plastic container. Repeat with remaining jelly crystals and remaining water. Place in the fridge for 8 hours or overnight to set.
Grease base and side of a 20cm (base measurement) round springform pan and line with baking paper. Process biscuits in a food processor until finely crushed. Add butter and process to combine. Use a straight-sided glass to press mixture firmly over base and side of pan. Place in fridge for 30 minutes to chill.
Process the cream cheese and condensed milk in a clean food processor until smooth. Place the extra boiling water in a heatproof bowl and sprinkle with the gelatin. Stir until gelatin dissolves. Add to the cream cheese mixture and process until well combined.
Transfer jelly to a clean work surface. Cut into 2cm cubes. Arrange one-quarter of the jelly over the biscuit base. Pour over one-third of the cream cheese mixture. Continue layering with remaining jelly and cream cheese mixture. Arrange remaining jelly over the top. Place in the fridge for 6 hours to set.