The thing is, nobody got faster, stronger, longer, while riding a bike. As a matter of fact you are worse off after you are done than when you started. You get faster, stronger, longer, while resting and giving your body a chance to rebuild itself.

Then again, this applies mostly to maximal effort. If you are a newbie at distance, improving comes so readily that maximal effort can't even be measured; you can indeed improve that fast.

As long as you are feeling fine go for it. Eventually you will over train and that's not the end of the world. At that point rest as hard as you train and you'll start improving once again.