mex,
To begin with, some clarification. The Cinque Terre is not a destination per se. It consists of five small towns and you'll have to specify your destination town when you buy tickets.
I've made that trip a number times, and it will be pretty much a full travel day. Using Interlaken Ost and Monterosso as the departure and destination stations, the easiest solution is a departure at 07:29, arriving at 15:05 (time 7H:36M, 2 changes at Spiez and Milano Centrale). There are numerous other solutions but they're longer or involve more changes.
You can check all solutions using the Bahn.de website, but they don't sell tickets for trains originating outside Germany. If you wish to buy advance tickets, you can use the SBB or Trenitalia websites, or a reseller such as www.trainline.com (I don't believe they sell tickets for trains within Switzerland yet.... you should be able to buy tickets for the entire route at the station in Interlaken Ost).