It looks like Timewalking in World of Warcraft Shadowlands will require you to be level 50.
In a post on the official World of Warcraft forums by Kaivax, questions surrounding how Conduits work in the new Shadowlands expansion were answered. The clarification comes in response to many questions' players had been asking since Conduits were announced nearly 2 months ago.
A recent interview with World of Warcraft's Ion Hazzikostas has provided some additional information on Conduits and more.