The duration of the route is provided with the route information. The calculation of the duration is based on an average speed that depends on the chosen route type.
If the duration of the route is far from your expectation, check whether you chose the correct route type and the correct routing. The duration of a 100km road bike route will be lower than the duration for a 100 km recreational cycling route.
Can I adjust the duration of my route?
No. You cannot adjust the duration of a route. That is derived from other factors, with length & route type being the two most important factors.