"only thereafter" is a correct and usable phrase in written English.
It means "only after that" or "only at that point in time." Example: The students were not allowed to leave the classroom until the bell rang, and only thereafter could they play outside.
Only thereafter, on March 18, did the Yugoslav regent, Prince Paul, and his ministers Dragiša Cvetković and Aleksandar Cincar-Marković agree to Yugoslavia's adhesion to the Axis.
The divine essence in purest form was conceived as vak (Sanskrit: "sound"); it developed secondarily into sacred sounds, such as AUM, and only thereafter into coherent words.
It was only complaints about the excessive exuberance of some of the feasts that eventually led the early church to ban them and suggest that the faithful should eat at home with their families instead and only thereafter gather for a symbolically spiritual rather than literally carnal banquet that we know today as the eucharist.
Only thereafter was he showered with accolades at home - the Howells Medal for distinguished fiction from the American Academy of Arts and Letters, the National Book Award for his Collected Stories, and the Gold Medal for Fiction, again from the American Academy.
Only thereafter do we turn our attention to matters of evaluation.
In order to test non-instantial theories, such as Newton's theory of gravitation, first empirical generalizations must be derived from them with the help of auxiliary hypothesis, and only thereafter can they be tested by inspection (Feyerabend 1962, 28).
A compromise might be to use branded ink during the warranty period but thereafter only for colour if you want top-quality colour photos.
There was Carter's claim that Reagan favored voluntary Social Security, a position Reagan had advocated in 1964 but thereafter only said should be studied.
He preached only occasionally thereafter.
Only occasionally thereafter did he play criminals, though his heroes invariably had a dark, complex side.
The only shock thereafter was that the 29-year-old did not complete a hat-trick.
