I got a 60 day extension eVisa from USA, good to Oct 20. I was told by supposed authority I can go in to immigration and apply for my 30 day extension as early as next week and immigration will put start date of the 30 days at October 20th. My only previous experiences was with Covid extensions and the start date of the new 30 day extension began the day you applied, no matter how many days you had left on your current visa stamp
Please, only requesting replies from people who have been down this road.