To be honest I'm not really sure why people want 24h races. Having done both the Le Mans and Nürburgring back in GT5 they're not something I'd call fun even though the sunrise on the Nordschleife still ranks among my best gaming memories because then I knew the 12-ish hours of pitch black darkness was over.
In real life a 24h race is a test of driving pace, driver endurance, pit crew skill, mechanical longevity and what not, a true test of the team as a whole. In GT you know whether or not you're going to win it after the first hour and then it's just 23 hours more of driving to be done. Now a 4h version, done in the same way as the Spa 1h race, that kind of a thing I could get behind but the full 24h version is just pointless without mechanical issues, potentially race ending damage, all the random things that make the real race what it is. Not to mention that doing the entire distance alone is just wrong.