Where I live a car makes an average of 60km/h, outside of a city. It's often faster, and does no in-between stops. So it's 10min. And I do commute by train. 8km. And it takes 45min door to door. These are real-world numbers. Living in the city and using the train costs me more than one hour of additional commute each day.

For comparison: It takes 25-30 min to ride by bike, depending on effort, weather, etc.