Musk spoke of 24-hour Falcon turnaround as early as 2011 and as late as 2019.
The fact that it's required for Artemis to work, and the amount (nobody knows exactly but lower bound is like 15) of Starships required to launch in quick succession just highlights how risky, to the point of unsoundness, the project is.
If you do the thermal design right, possibly use a sun shade (space is a large thermos bottle after all) or even use active cooling to remove the little heat that gets through, then it should work just fine. :)