If I were travelling that route, I'd probably use this method.....
- 09:03 - Bus from Munich Hackerbrücke to Zürich Carpark Sihlquai, arriving 12:45.
- Walk from the Zürich bus stop across to the main rail station (you can see it from the bus stop, not a difficult walk).
- 13:02 - train from Zürich to Bern, arriving 13:58.
- 14:04 - train from Bern to Interlaken Ost, arriving 14:57 (it's the second station in Interlaken).
- 15:05 - train from Interlaken Ost to Lauterbrunnen, arriving 15:25. Be sure to check the small digital display on the side of the Berner Oberlandbahn to ensure the end destination is Lauterbrunnen and not Grindelwald.
- 15:35 - Post Bus (bright yellow, you can't miss it) from Lauterbrunnen station to Stechelberg, arriving 15:47.
- 15:55 - Schilthornbahn cable car to Gimmelwald, arriving 16:00.
There's a similar (but not exactly the same) departure leaving Munich at 06:33, that will get you to Gimmelwald at 13:30. I always like to enjoy the breakfast I've paid for at the hotel, so prefer departures after 09:00. There are numerous other departures, with longer travel times. You can see all the solutions on the Bahn.de website.
If you decide on the earlier departure, head to the Munich station early and pick up a sandwich & coffee (or whatever) for breakfast. There are lots of food stands in the station.