Obviously, it cannot be faster than the speed of sound.
So, indeed, if we were at around 200 km, the sound could not have reached us after 4 minutes.
I am 67 years old, and this happens 45 years ago: obviously my memory is failing.

4 minutes at the speed of sound is around 83 km.
We definitely were farther than that.

I am convinced that the 200 km are correct. So the sound must have reached us 10 minutes later, not 4.

Thank you for pointing to my mistake.