Excursion to the Rhine Falls.

We will be arriving from Amsterdam, will spend our first night in Switzerland in Zurich then the next day, plan to visit the Rhine Falls After spending time at the falls, we will travel on to Interlaken for 5 nights. To give our B+B host some idea of when we will be arriving, how long should we realistically be expecting our excursion to the falls to take? Thanks in advance.