This is common sense advice. If the event you are aiming for requires you to ride for three days at a time, then make sure in your training that you are completing three day blocks.
The ideal time for this is across a bank holiday weekend, where you hopefully have the option to get out for three longer rides on consecutive days. You could almost treat it as a mini training camp. It isn’t always possible (or productive) to do three long rides back-to-back in training so aim to ride on all three days but increase the intensity on one or two of the days and reduce the length of those training sessions.
However, I wouldn’t advocate extending your training blocks for longer than three days at a time without a recovery ride. Doing this will likely mean that you come of out the block too fatigued and you will require a big block of recovery. Going back to the first point, this will impact the consistency of your training. As with any training, it’s a case of balancing your workload and recovery as it’s during your time off the bike that you make the necessary adaptations to training.
A much better way to plan your training is to do two three-day blocks separated by a recovery day in the middle. What should a recovery day involve? You can read my previous article. This gives a big week of training but manages fatigue levels so you shouldn’t finish the block on your knees. Tour de France riders don’t go out and ride as hard as they can for 21 days in the lead up to the Tour, likewise you don’t need to do six five-hour rides back-to-back to prepare for a week-long sportive like the Haute Route.