Given the most favorable case for survival, and assuming that enough
Challenger remains were or could have been immediately recovered by
search and rescue teams, for how long after the main blast could an
autopsy have precisely determined time of death?

Would such an autopsy have been necessary within a matter of days, or
hours? Could it have determined time of death to the nearest minute?

To what end?


Its already known. The time oif impact of the crew cabin to the water.

We know some crew managed to turn on their emergency air supply. So they likely
klived to impact. At the speeds involved no one could of survived.