According to Official Guinness Records,
The fastest time to flip 10 cars on their roofs by a team is 52.07 seconds and was achieved by Matteo Armellini, Fabrizion Zandonai and Enrico Brusco (all Italy) on the set of Lo Show dei Record in Rome, Italy, on 11 March 2010. Each car weighed at least 500 kg and had handles attached to it for a better grip. The record was part of the Italian TV show "Lo Show dei Record".
For a complete list of 2010 records, please visit 2010 Guinness Records in Italy.