Like any gamer, the notion of spending 12-24 hours in game was something quite natural. Of course, when work, family, and studies are among the many other responsibilities that cut into your game time there comes a whole other perspective to the games that last more than a day's worth of work.
I've observed this with my GM, who is a family man and working. His games are roughly 4-6 hours long, his total opportunity cost consists also the traffic of metro manila that makes 1.5-2hrs drive over just 9-10km (6mi) from Makati City and the hours drive over 16-18km from the game to his home at around 12mn. This makes roughly a total of 6.5-8hours opportunity cost.
The problem with 8+ hour game is that it doesnt work when you have a lot of responsibilities. More importantly, when you are very much aware of productivity and catharsis (aka Fun) matching values in your own life, you want to cram as much fun in those hours as possible.
There is a tempting draconian perspective how one can enjoy the game. There is also an enlightening level of maturity and awareness that comes in a certain age where we understand what we like about it and are able to minimize the waste and maximize the fun.
Factors that Affect Fun/Time.
Materiality (in accounting) is a doctrine called de minmis non curat lex which means basically we don't pursue trivial matters. That's pretty much the underlying source of some game time waste, and requries a measure of experience and memory for matters.
Hirits. I know some games where some players and gms (I admit to like this too) always want to get a word in. In tagalog these "witty" remarks, teases, and side comments are called "Hirit" (pronounced like "hear-it" very quickly). Hirits are a natural part of any game, there is fun in it as well as, sometimes, it is what makes a particular game momment memorable and incredible. The problem sometimes is that Hirits can be plain disruptive. Most of the time, the will power to control one's urge to hirit depends on the participant's mood and how day went.
Fixing this problem is quite as simple as enforcing discipline by example. The GM and even the Player, can casually explain to the group that they are pressed for time and would like to keep Hirits to a minimum. Other social techniques maybe required to get this level of discipline across, consider it part of the GM's job description. The bottom line is fun, when the whole group can agree before hand how the excess is disruptive to their enjoyment, their own stake for their enjoyment would be motivation enough. If that is not enough, the GM should re-examine the party's own payoff matrix for their game (to max out fun).
Organization. Game Prep is a seperate matter from running a game (since it occurs before the game). An organized approach, is something typically overlooked. Organization doesnt just mean arming one's self with the flow of narrative and action. It is also the development of a set of benchmarks, items and challenges.
Interestingly, the skills of GMing is also useful in a boardroom (and in any time orginzation can occur before action) when you can cut straight to the heart of the matter and arrange the flow of ideas in the most efficient manner. Once mastered all the other add ons are just story telling dressing where the Art level of skill arises.
As there are other GMing books and tips can be found in the web and print, I would highly recomend those books developed by credible business schools (which is more highly refined in my opinion) in conducting meetings, discussion, and communicating ideas as a contrast. The skills that are used in GMing, and for the Player's the problem solving, are part of a integral set of important skills that is used for work. These skills have a huge body of knowledge to draw from, and it would be such a waste not to draw from them.