According to Official Guinness Records,
The longest yoga lesson lasted 56 hrs 57 min and 21 sec and was achieved by K.P.Ranchana (India) in Chennai, India, from 19 to 21 June 2017. 36 Participants took part in the lesson for the duration in order to set this record.
For a complete list of 2017 records, please visit 2017 Guinness Records in India.