A well-balanced training schedule includes long, steady workouts as well as shorter, higher-intensity sessions.
In summer, the variation is added easily enough, especially to a bike commuting schedule, simply by riding a longer route one day a week. But in winter my available training time tends to be the same length all the time, an hour or less. That eliminates the nice, long burns that really seem to give all the training a broad, solid foundation.
Long, steady workouts are also good for scouring out the accumulated fats from a somewhat self-indulgent diet. I just haven't learned to restrict myself to purely nutritional foods and spring water. And don't look for it to happen any time soon. Even if I was reduced to Dumpster diving, I would probably do some of it behind candy stores as well as better restaurants and grocery stores. What can I say? Life is to be enjoyed.
Even at an hour a pop I can stay ahead of the worst of the flab in ski season, because cross-country skiing uses every muscle in the body. That uses up plenty of fuel. If I keep the output moderate I can still mobilize fat reserves rather than burning only recently-consumed carbohydrates. Plenty of coffee in my system helps liberate the stored fats.
Coffee. What can't it do?
Some people can't handle too much of the nectar of the bean. They'll have to find other ways. Certainly if the opportunity comes along for a three-hour, low intensity workout, the body will dig into reserves anyway. Add hours as you can, for more thorough depletion. It's like eating the leftovers out of the fridge, except you don't have to worry about which ones are moldy.
Remember: anything is better than nothing at all. Twenty minutes a day is a lot better than a sudden two or three hour slam on a Saturday or Sunday.