The Reserve Bank of India Bill was introduced and passed by the Central Legislative Assembly in December 1933.
Assent & Becoming an Act: After passage, the Governor-General gave formal assent, and it became the Reserve Bank of India Act, 1934 on 1st April 1934.
Establishment of RBI: Following the Act, the RBI was officially established on 1st April 1935.
So:
Bill passed by Assembly → December 1933
Act formally enacted → 1st April 1934
RBI established → 1st April 1935