That would be correct, yes the heat transfer would be transient... I am assuming that the combustion process is steady state, hence, constant inner wall temperature, with outer wall temperature a function of time.
Suppose you have a cylindrical rocket engine with surface temperature T and you want to measure temperature on the inner wall T0 of the combustion chamber (assume 1 dimensional heat transfer). The chamber has thickness d, and heat transfer coefficient k. If combustion is assumed to occur...