When to cancel no cost EMI to avail interest benefit?

Dear dimers?

I placed an order on amazon using no cost EMI offer on my HDFC regalia first card. I got upfront interest component as discount as it would be billed on card later.

My question is, when should I cancel the EMI and convert it to normal transaction? Can I call to HDFC and request for the same immediately or should I wait for a week?

I received an email from amazon after placing order and it says this
“1) Within 4-7 business days, your bank will reverse the charge of ₹——— and convert it into EMI. Initially, your card will be blocked for ₹ -—- and with each installment you pay, your limit will get released.”