Well technically this was not the republican convention was it? This was a separate speech.
Speech was called “A TIme For Choosing” and it was given October 27, 1964 - about a week before the election. While this speech did not do a whole lot for Goldwater (he was to lose in a landslide), it did get Reagan noticed and launched his political career. He would be elected governor of California two years later and the rest is history.