The three-four time signature is frequently used in swing music or dance music. But what was the first rock song to use this time signature?
Might depend on what you consider 'rock' & whether 6/8 would sneak in as 3/4- but how about The Animals, House of the Rising Sun. 1964.
Or Moody Blues - Go Now.
Beatles - You've Got to Hide Your Love Away. 1964.
The trouble with the 60's is rock hadn't quite been invented yet, so the answer might turn out to be Hendrix.
Three I can think of, in ascending order of both rockiness and release date
Bob Dylan - The times they are a changin' (1964)
The Beatles - Norwegian Wood (1965)
Jimi Hendrix - Manic Depression (1967)
I'm not sure if the first two are really 'rock', and the I can't remember if the last one sticks to its 3/4 guns all the way through.
Screamin Jay Hawkins I put a spell on you (1956) also has a triple-time feel, though online sources disagree on the actual time signature. Again, maybe not really 'rock', though the vocal delivery is rockier than most...