Those are general recommendations based on what your body may be able to absorb within a given timeframe. You won't be able to replace every single calorie burnt during a ride like that (nor would it be practical). You also have to factor in pre- and post-ride meals, burning fat for fuel, etc.
On your long rides, start replenishing calories within the first hour, and see how you feel then (i.e. don't wait until almost three hours and only then begin consuming calories.) That's a good first step and the results can inform future decisions on in-ride fueling. It could give you another hour, maybe two more hours. It could also show you the limits of your muscular endurance. There's so much to learn!