Obviously (the excellent) William James predates this by some time, but within the context of the modern era, this sort of thing has been discussed long before the Hallowells and Ferrisses of the world made their careers by repackaging old notions.
But in 30 minute increments: 30 minutes heading toward Las Vegas, then 30 minute heading toward San Diego.
Multitasking is not just switching between tasks. It requires tremendous effort and time to achieve it, but it can be done.
There are certainly areas where some level of multitasking can be trained. For some, it's still merely fast switching, and for the gifted few, there's the capacity to become so familiar, competent, and therefore at ease with complex tasks that they become second nature, and that frees up bandwidth for other things.
The problem gets to be that that sort of thing is very challenging, and most people just aren't capable of doing it well, if at all. The level of self-deception surrounding the issue is stratospheric. (We're talking about maybe ~5% of the population.) And, for the most part, it only makes sense to practice in high-workload environments where there may not be the ability to add people to divide the workload (think: some aviation).