I also have time constraints, which has limited my workout time to a hour a day, except on Sundays. I think any workout can be a good one as long as you pay attention to your heart rate and push yourself, whether it be for speed or distance. I also think it important to mix up your workouts, and not stick to just one thing all the time.
My current WO schedule looks like this:

Tuesday: Bike 1 hour (work on speed and intensity)
Wednesday: Swim <1 hour
Thursday: Run <1 hour
Friday: Recovery day
Saturday: Bike 30-45 min.(easy) + short run
Sunday: Bike 2+ hours (work on time and distance)
Monday: Recovery day

Right now I am just building a foundation in all three disciplines, so I can start training in earnest next year. The guy who will be my coach told me that speed and distance figures mean nothing right now, except in relation to my own previous efforts. I think as long as you push yourself in whatever little time you have, it's a good thing.