It takes you 20 minutes to drive... how far, and how fast is your car going? How fast can you ride a bike (average speed for the route you choose)?
If it's 20 minutes at 30 mph, then you are talking about a distance of 10 miles. Now, that can be a smooth, flat 10 miles, or it can be 10 miles of up-and-down hills. Even a stiff headwind on a bike will slow you up, while it won't affect your car's speed a whit.
On the other hand, 20 minutes at 60 mph is 20 miles. That will take a while on a bike, even on a flat route. If you can hold a speed of 15 mph the whole time-- and that's a fairly brisk pace, particularly on a heavier bike-- it will still take you an hour and 20 minutes. With hills, or a strong headwind, it will probably take a lot longer.
Then again, as another person said, in heavy stop and go city traffic, a bike might be faster than a car. In that case, it might take 20 minutes to go 4 miles in a car. That's 12 mph, while your 15 mph bike can make the trip in about 16 minutes or so, not accounting for traffic lights.