The temptation of time-pressed trainees is to combine short runs into a mini-long run on one midweek day. Don’t do it. Doing another long run each week can only negatively impact your Saturday run, and may lead to overtraining and/or injury. Far better, in my view, to run 2-3 miles of hills, or 2-3 miles very fast, a couple times a week, to rack up your mid-week mileage. EFFORT, not distance, is the touchstone of midweek training. Because the runs are short, midweek training can be a lot harder, physically and mentally, than the Saturday long run. On Saturdays, the distance, alone is the challenge, especially for the new runner who with each long run, is setting a new lifetime maximum distance. If you must work on speed, do it on short midweek runs, and work on your endurance on Saturdays.