Assuming we're talking flat roads, the average speed for mountain bikes with standard knobby is around 15mph so it would take you 1hr and 20 min.
The average for road bikes is around 20mph so it would take you 1hr but if you don't ride often I would estimate an average speed of 15mph and total of 80 min.
For experienced riders speed can go to 30mph which means it would take you 40 min.
As you can see, it's all about the average speed that can be maintained and the results can vary significantly
