It somewhat depends on your age and current level of fitness. Keep in mind that pro bicycle racers take days off and winters off.

There is also a growing body of study indicating that daily moderate exercise (in bicycling this is about 30-60 minutes @ 13 mph) is better for general health than strenuous exercise, particularly for people past about 35. If you get a lot of enjoyment out of racing or riding with fast groups every day then that's one thing and the enjoyment is beneficial in itself, but if a longer life in good health with as few ailments as possible is your goal then moderate is likely the way to go.