According to Official Guinness Records,
The longest distance to stretch home-made slime in 30 seconds is 2.23 m (7 ft 4 in), and was achieved by Ciela Villa (USA) in New York, New York, USA, on 1 February 2018.The attempt was overseen by Science Bob.
For a complete list of 2018 records, please visit 2018 Guinness Records in United States.