To me less is more: 3 hours. 6 hours is too short to be "epic" like LM/Sebring/PLM, but too long to create better racing. And seriously 6 hours of day often feels like a burden and it is simply a nightmare for tv. When the biggest purists are calling even 24 as a sprint, what is the point with more then?
Now I am going to run and hide as I am sure this is a minority opinion.