According to Official Guinness Records,
The longest chanting marathon is 24 hr 10 min 8 sec and was achieved by a team directed by Sri Ganapathy Sachchidananda Swamiji (India) in Frisco, Texas, USA, from 31 July - 1 August 2015 582 attendees at the Hanuman Temple in Frisco, Texas, were led in the chanting by worldwide Guru and spiritual leader Sri Swamiji.
For a complete list of 2015 records, please visit 2015 Guinness Records in United States.