3-4 hours. I may add some 5-6 hr rides once a month, (approaching century), but I generally find them too boring. My observations come a little more from gym work-outs that tend to be more..dynamic. I warm up running a 5k, then do a BOSU work-out or drop into a class, like kick-boxing or spin.

I don't think you're right about "the glycogen reserves are stunning". I think exactly the opposite is happening.

Maybe, I don't know that answer for sure & I have an open mind. But I have been reading about training and diet greatly impacting glycogen reserves, like 1000% improvement, and my subjective experience seems to bear that out. I say that because pretty much all the peak and valleys are gone, daily energy is constant state morning afternoon & night. Eating in the evening doesn't much change anything, working out in the morning or evening isn't much different. If you are correct, then I would expect to experience a glycogen bounce after the 6pm meal, feel like pounding it out late night, early morning. Never happens. Occasionally I'll fuel with a Cytomax drink before a tough gym workout, but that doesn't seem to make much difference either. The most empirical explanation seems to be: glycogen is on a meter, no peaks, no valleys.