As far as I understand, Turing himself did not specify a duration, but here's an example paper that ran a randomized study on (the old) GPT 4 with a 5 minute duration, and the AI passed with flying colors - https://arxiv.org/abs/2405.08007

From my experience, AI has significantly improved since, and I expect that ChatGPT o3 or Claude 4 Opus would pass a 30 minute test.