CYCLING PERFORMANCE TIPS
I'd never read about the "within-day energy deficiency concept, but the logic makes sense and the original study gives evidence for negative metabolic effects of a short term Caloric deficit - even when the total Calories for the full 24 hour period balance out.
That study documents "..a significant correlation between the largest single-hour calorie deficits and hormonal disturbances like lower testosterone and higher cortisol." The question is whether that is really a bad thing.
Laboratory studies show animals subjected to fasting and semi starvation diets live longer. So a lower metabolic rate may actually be a good thing in the long run. But I doubt it is good for an athlete-in-training who needs to keep their body's repair processes at peak efficiency.
If you want to compete at your best, you need to train at your best. And anything that limits your interval (or HIIT) sessions is harmful to that goal. That argument is similar to the reason athletes who are going to compete at high altitude train at lower altitudes.
There is an argument that depleting your muscles of glycogen (the prelude to this deficit) has a positive impact by up-regulating fat metabolism and "forcing" the body to get used to burning fat instead of carbohydrates for energy. But are the benefits of that metabolic stress outweighed by the total body stresses (and impaired reparative processes) from intermittent periods of caloric deficit?
I am not a proponent of training on a low carb/high fat diet and can't think of any downside to moving a higher percentage of Calories earlier into the day. It seems to have no risk and only an upside potential.