Rhine falls

Yes, you could manage that. The following example assumes you could be ready to catch a 9:00 am train at Interlaken Ost or 9:05 am at Interlaken West. The fastest route with the least connections is the IC 964 to Bern and then the IC 813 to Zurich airport. It takes 2 hours an 16 minutes, getting you there at 11:16 am. Give yourself at least an hour to check your bags and return to the train station. But you might as well take an additional half hour to grab a quick bite because the best train to the falls is hourly. At 1:01 pm take the S16 from the airport train station in the direction of Herrliberg and get off at Oerlikon station 5 minutes away. Then catch the S9 at 1:15 pm in the direction of Schaffhausen and get off at Neuhausen Rheinfall at 1:57 pm. At the train station platform if you walk to the rear of the train you will have a great view of the falls. Don't walk down from here. Walk along the platform in the direction of the front of the train and you will find a bridge out to an elevator that takes you down to another elevator that takes you down to the lower level of the falls. From there it is a 100 yard walk to the riverfront viewing and the boats if you want to ride them out to a rocky outcropping in the falls. The S9 leaves one minute after each hour and half hour and takes about 43 minutes to get back to Oerlikon station where you can take a S2, S16, or S24 back to the airport. Each takes about 5 minutes.

I am just wondering if it might be simpler to go from Interlaken to Zurich Hbf and store your bags there as there are banks of luggage lockers of all sizes there. You could do that in about 10 minutes, then get the S-9 to Neuhausen-Rheinfall. Those direct trains go at 7 past the hour and take 50 minutes. Return direct trains are at 1 past the hour and after 16:00, they go every 30 minutes (at least on week days). Get the bags out of the locker at Hbf and then trains to the airport are every 10 minutes or so.