I HIGHLY recommend completing shorter workouts most days of the week. Then, it becomes a habit and it's short enough to rid you of any excuses not to do it. 20-30 minute circuit training gets your heart rate up and burns calories.
The workout below will kick your butt (literally) in 20 minutes. I recommend 5lb. hand weights. But if you're a beginner, don't use any. Trust me, you'll still feel it.
Do it. You'll feel good.