Payment plan and CA wildfires extension

I am in Los Angeles and filed by April 15 and asked for a monthly payment plan. I provided my bank details so the payment would be deducted automatically. I later received the notice that our tax deadline had been extended to October 15, including payments. I thought the IRS would begin debiting my account on the new deadline but I just noticed they took the first installment this week, in August. Can someone explain how they decide the date to begin the plan?