Definitely over-promoted as a way to instantly increase your fitness. Take a kook at actual dietary science and you'll find it takes 1-5 hours (simple carbs to complex proteins, respectively) for your body to digest anything into a form usable by your body's cells, so 1-2 hours rides shouldn't be an issue as long as you east a balanced diet, maybe throw in a few extra carbs if your weight drops due to ongoing cycling activity.
Better is to get in shape and keep hydrated in hotter weather. Do an occasional session of sprint intervals (or hill repeats) to 'up' your anaerobic fitness level, push some sections on a long distance rides, and you should see improvement. Dehydration will wear you down faster than lack of calories if you're eating a balanced diet, so don't be afraid to drink water regularly, especially if you're riding in warm weather - a little too much is far better than too little.