At 54, I know I can't do what I was able to do 10 and 15 years ago whether it be with skiing, cycling or any physical activity. I ski much smarter than I ever did before partially because I have to but a lot because I am smarter and wiser today. How much quality, highly focused, high energy ski time do any of us have in us each day. If you look at WC racers who are arguably in the best shape of anyone in the world, they are on snow working hard for maybe 2.5 hours each day, max 3 hours of high energy, highly focused work. I think if you ask any of the top PMTS skiers (Harald, Diana, Jay, Max etc) how many hours they can go full out, in tight high energy turns on piste or off, I doubt any would say more than three hours. I find i max out somewhere between 2.5 and 3 hours if I'm going quite hard and if I go 4-5 hours real hard I won't have a lot in the tank the next day.
Ideally I would love to be on snow 5 days each week for around 2.5 hours each day. This is pretty much what Geoffda and the rest of the Keystone/A-Basin gang do. They ski every weekday for 1:45 or so and the head off to their jobs, lives etc. It's pretty much what Max has done for years, 5 days per week of skiing usually with none being much longer than 3 or so hours (big pow days and a few other occasions being the exception). There is no doubt this is the fastest way to progress.
I am using this model as my guide even though I only ski 40 days per year and they are almost always in packages of 5-15 days at a time. I have found many days this season that I have gotten a great result in 2.5 hours with some drill work followed by some highly focused high energy skiing (no cruising). In the past I would stay out and watch my skiing deteriorate as the day went on and often to come back the next day with less than quality energy for another days work.
Actually those of us that ski limited days and live a ways from the slopes, need to maximize our energy and focus more than those that live close and ski 100+ days per year. We are all adjusting to being at altitude (where we don't live) and even if you are in your twenties or early thirties, no one can slam it hard for 6-8 or 10 days straight and still have quality energy and or focus. All of us have woken up slammed from the day before at times.
For me the model is 2.5 to 3 high energy hours of skiing and if I go longer I know two things, my skiing will be deteriorating and I will in some way pay for it tomorrow. On a big pow day that's OK and well worth the price. (Yes we can all cruise with low energy, wide GS turns and stay on snow all day but IMO that is both a waste of snow and time, and some drill work can be easier on the body and can be done for more hours in a day).
Add to this the rule of skiing max 4 days straight without taking a day off (which all of us break at times) and you have the model for maximizing ones ski time. At least IMO. I'm sure someone will disagree with me!