Assuming that you have a really substantial aerobic base, speed workouts can be incorporated easily into your existing bike workout or as a separate training. For example on almost any ride, I like to add 5-10 "sprints" where I go up to 90% exertion for 10-20 seconds with 5 minute rests in between. You can also incorporate a separate speed workout for the bike that will be a series of 3x30 seconds and 3x1 minute at 90% exertion with rest in between. Total time for me on that is about 30 minutes of internals with a 20 minute warmup. These are just ideas and you would do well to buy Joe Friel's book "The Triathlete's Training Bible" or one of the other good ones for other workouts. There are also good plans on the web. Here is a link to the Trifuel plans http://www.trifuel.com/training/training-programs.

But, I would really advise you to make sure that your aerobic base is really strong before adding too much in the way of anaerobic work. A coach once told me that when I felt strong in the last hour of a 4-hour training ride in the hills (lots of hills around my house) and I was able to recover quickly, than I was ready to incorporate anaerobic workouts into my bike training for additional improvements.