My good friend is a former world ranked professional Marathoner and he shared a great training format with me a number of years ago. We were at a shoe expo and I asked him what he did to stay in shape. I figured since he was at such a high level for so many years he would tell me that he runs 5-6 times per week at various distances.
I was surprised when he said that he does two 25-35 minute runs per week and mixes in other things such as mountainbiking and cycling. He said that if you can do two runs per week, it gives you a simple and solid base of conditioning that keeps your body ready to go should you ever desire to do longer distances or other activities requiring much more duration and intensity. He said that if he ever decides to enter a running event, he is only a few weeks or months away from being prepared, depending on the event.
I have never forgot that conversation and have found that format to hold true with other forms of exercise such as weight training, various sports and disciplines of training. If you are consistently active and can maintain at least two days of that particular activity per week, you are basically ready to go because you are keeping your conditioning and skill levels sharp.
In addition to my biking and snowboarding activities, I mix in 2-3 days of weight training and 2 days of running each week and feel prepared to tackle numerous activities whenever I choose. I do one flat surface run per week and one leg burning, steep, trail-run per week and I have found it to be a great format for me.
Keep in mind that I do take longer runs here and there to push the limit every so often but overall, I always keep in mind that at the very least, if my week is really busy I can knock out two runs and/or two lifting sessions per week and not miss a beat.
Try the two-timer format and I am confident it will give you a mental edge as you push forward toward your goals!