Interlaken to Murren

You can look up all Swiss train times on the SBB website: https://www.sbb.ch/en
Interlaken Ost to Mürren, random date, time: 12:30

(1) Interlaken Ost dep 12:35, Mürren BLM arr 13:28
(2) Interlaken Ost dep 13:05, Mürren BLM arr 13:58
(3) Interlaken Ost dep 13:35, Mürren BLM arr 14:28

Train (1) is too early. (2) looks like the train which is the official connection from your incoming train. But it arrives in Mürren at 13:58. Technically you have made it, but where do you have to be in Mürren? How far is it from the station?

The train from Interlaken Ost to Lauterbrunnen where you need to go to catch the gondola to Grutschlapp and then the train to Murren currently leaves at 13:05 arriving at Murren at 13:58.

Thank you.

We are hoping to take the Golden Pass from Montreux that morning (we are landing in Geneva late the night before). We can get to Interlaken much earlier if we don't take the Golden Pass.

What will be missing if we take a regular train from Geneva - Interlaken? Would it be better to skip the Golden Pass and give ourselves some cushion getting to Murren?

Why do you need to be in Mürren by 2:00 pm? What happens if you are 5 minutes late?

If it is important, take an earlier train from Montreux. You can ride a regular regional train over the same tracks as the Golden Pass train. It just won't have the special cars but the scenery is the same.

What will be missing if we take a regular train from Geneva - Interlaken? Would it be better to skip the Golden Pass and give ourselves some cushion getting to Murren?

All rail routes in Switzerland have at least one train per hour, including the Golden Pass route (Montreux - Zweisimmen - Spiez - Interlaken).
When you look up train times on the SBB or any other rail planner, it always finds the quickest route (not necessarily the shortest, but the quickest). If you look up Geneva to Interlaken, it will route you through Bern, going round the Alps and taking approx 2h50. If you want to follow the Golden Pass route (either in the named tourist train, or on one of the normal hourly trains), you need to add "via Zweisimmen".
I did a search Geneva to Mürren via Zweisimmen:

Genève dep 04:51, Mürren BLM arr 11:28
Genève dep 05:39, Mürren BLM arr 11:28
Genève dep 06:30, Mürren BLM arr 11:58
Genève dep 07:30, Mürren BLM arr 13:28
Genève dep 07:39, Mürren BLM arr 13:28
Genève dep 08:30, Mürren BLM arr 13:58 <-- The train connection we were discussing earlier

So yes, there are earlier trains if you are prepared to leave Geneva earlier. Or, you can go by the quicker route via Bern, instead of the scenic Golden Pass route. The slow scenic Golden Pass route is costing you an extra 2 hours.

When are you taking this trip? On the SBB website it says:

Construction work: Montbovon - Château-d'Oex
Between Montbovon and Château-d'Oex, no train services are operating.
Replacement bus services are operating Montbovon - Château-d'Oex.
The transportation of bicycles and of wheel chairs is not allowed. The connections are not guaranteed.
Duration from 13.03.2018 05:00 until 02.06.2018 05:00.

Thank you. This is very helpful!

I'm re-waking this post... Thank you for all the help so far.

We decided to take our chances with the Golden Pass route, so we'll have 15 minutes to make our connection in Interlaken OST. Is it worth purchasing our tickets for Interlaken to Murren ahead of time or can we get them when we arrive? Thank you!

Why wait until Interlaken Ost to get those tickets? There's a chance of a long line for tix at that station, and then you'd miss the next train. (They go every half hour to Lauterbrunnen.)

If you are buying your Golden Pass tix in Geneva, just ask them to add on the Interlaken Ost to Lauterbrunnen "any time" tickets. They speak perfect English there so they'll know what you mean.
(Most Swiss tix are "any time" that day tix, except for the few that are on sale and pre-bought.Those sale tix, or reserved seats, are only good for the time specified.)

Thanks, Shoe. That's good advice!