A lot of us head to the gym and spend about 45 minutes on the bike while reading a book or magazine and working moderately hard. I am not knocking this behavior, since I am happy when anyone makes time for the gym, but one day a week try and do a good, quality workout. This means making everything you do count by really pushing yourself to get through it and working your hardest, i.e. you shouldn't be able to focus on a book.
What's more? Since you are going for quality (not quantity), you may even find that you can do fewer sessions while getting the same (or even better) results and ultimately saving time. Now who doesn't love saving time? Try it out and let me know how your quality workout went.