Golden Pass transit times are short because of different track gauges - widths - everyone has to get off one train in say Zweisimmen and get on a waiting train to go on via wider-gauge trains. No problem. And a Spiez if you miss one train to Interlaken another will leave within a half-hour IME - put angst to rest.

"And at Spiez if you miss one train to Interlaken another will leave within a half-hour IME"

wrong!

20 min later! It's just the direct Zweisimmen - Interlaken train starting at Zweisimmen after the arrival of the Golden Pass train leaving Montreux at 15.44

(Dianedancer wants to leave Montreux 1 hr earlier, at 14.44 by slow train, with a 15 min layover at Gstaad).

"And at Spiez if you miss one train to Interlaken another will leave within a half-hour IME"

wrong!

20 min later!>

To me 20 minutes is within a half hour! How can that be wrong?

anyways IME Swiss trains don't run like they are rumored to - like clockwork being right on time - I've noticed late trains many times and not just a minute or two - they usually will IME hold up a departing train a bit for a late train but not always.

Nothing is wrong; there are just many Spiez - Interlaken trains in this tie frame:
Spiez dp 17.03, 17.09, 17.33, 18.05, 18.25, 18.33.....
mostly because people who live at Interlaken go home from Berne or Thun (after work or shopping) at this time.

that's my point - don't owrry about transit times in Spiez to Interlaken - trains all the time, miss one, hop the next - tickets or passes valid on any of them