Kevin,
That particular trip is a bit lengthy, but not too complicated. Several train changes are required, so be sure to pack light as you'll probably need to use the "sotto passagio" (tunnels) to get from one track to another!
The shortest trip I could find departs Interlaken Ost at 07:29, arriving Manarola 14:34 (7H 5M, 4 changes at Spiez, Milano, Genova & Sestri). Note that three of the trains require compulsory reservations (should be OK to buy when you arrive at Interlaken, unless it's a holiday or whatever). Also, this route is not covered every day (probably not Sunday?). Check the www.bahn.de site for all the details.
One word of caution. If you choose this trip, be "prepared for" Milano Centrale. It's one of the most chaotic stations I've encountered so far (not sure the best word to describe it?).
Hope you have a great time in the Cinque Terre!
Good luck and Congratulations!