Instantaneously rhymes with:
contemporaneously, erroneously, extraneously, harmoniously, simultaneously, spontaneously, unceremoniously, contemporaneously, curiously, enviously, erroneously, extraneously, furiously, gloriously, harmoniously, hideously, hilariously, indubiously, laboriously, mysteriously, notoriously, obviously, precariously, previously, seriously, simultaneously, spontaneously, studiously, tediously, unceremoniously, variously, vicariously