The value of very long practice sessions probably depends at lot on the skill you're trying to acquire. If it's a mechanical/physical skill, then the muscle groups involved would be a big limiting factor, especially for novices. Playing guitar would be challenging for a novice to practice for more than half an hour while people of average physical ability could practice a golf swing for an hour or more on day one.

The problem with favoring long sessions is that you can fall into the trap of only doing long sessions because of the perceived efficiency. Which means you'll need to 'make time' for it. Which means you'll put it off. The result is that most of the gains you make will be lost by the next time you find time for another extended session.