I don't think so. I used to think it was quite early, but there is enough evidence to suggest that a) the Church in Kerala was what we'd call Oriental Orthodox following the East Syriac Liturgy until the advent of the Portuguese, and b) that the establishment of an outright "Nestorian" jurisdiction is a 19th-20th century phenomenon related to jurisdictional squabbles in the Syro-Malabar Catholic Church.
I believe you and I'd love to see that substantiated. Not that I doubt you, but I'd just love to have something approaching solid proof so I could contradict all the Western historians who write otherwise and contend that the Church in India was Nestorian until the hook up with Antioch.
The same Western historians who say St Thomas never came to India? This article
is certainly not the equivalent of digging up a stone tablet from the seventh century which says "We are not Nestorians", but it presents some interesting facts.
Certainly it seems to be the case that the Assyrian Church of the East in India was born out of struggles within the Syro-Malabar Catholic Church. For the Western historians to be correct, this would mean that
1. The Indian Church was "Nestorian" for a thousand years or so.
2. When the Portuguese came, "Nestorianism" completely disappeared, replaced by Chalcedonian Christianity (specifically, RCism) and Orthodoxy.
3. When the British came, Protestantism was introduced.
4. And around the same time, a group broke away from the Syro-Malabar Catholics and became "Nestorian".
Can the Western historians explain how the Church could be "Nestorian" for so long, only to have it disappear so thoroughly for two or three centuries before it came back? It wasn't like the Christians had no way of getting to Persia if they could get to Antioch, Alexandria, and even Rome.