Keep track of the number of minutes or miles you walk and, each week, attempt to surpass the previous week's total. Strength is the cornerstone of everything we do. Without a solid base of strength, our daily activities are more difficult and we're more prone to injury or disease. Strong muscles will help you accomplish your aerobic exercise goals by helping you walk faster and climb bigger hills. Often, if you have difficulty riding a stationery or real bicycle, it is due to a lack of leg strength not a lack of aerobic endurance.
Strength training produces strong, firm, lean muscles and strong bones.
This means that you should be stopping at 10-12 reps because you can't do anymore, not simply because that is the number you've been told to do. To lessen the demand on your time, you could divide these exercises into different workouts. Instead of trying to work your whole body in a single session, which could take a little while, try breaking the exercises into upper and lower body days. Two days per week you do your upper body exercises and two days per week your lower body. Again, to truly reap the rewards that exercise can provide, one needs to challenge the body to change.