At the beginning of their career, The Jesus and Mary Chain refused to perform for more than 20 minutes becuase "no one in history has ever perfored a rock show that need to go on any longer than that." (and I paraphrase a bit due to hazy memory)

90 mins is acceptable for a headliner, but personally I like to see a headliner on for 2 hrs or more. Unless they are a new cat and can't fill that much time.