>> Mon May 14th Frankfurt to Lauterbrunnen
That should work well. If you pick your connection carefully, you can probably get a service with only one change (at Interlaken Ost). The trip will take about 5.5 hours. You can see what the options were for May this year on the Deutsche Bahn website:
The Deutsche Bahn timetable for next year will be released on 17 October 2017, after which time you can check the options for your actual travel date.
>> tues may 15th lauterbrunnen, Wednesday may 16th lauterbrunnen
When you go to Wengen, there is a great lookout you should not miss! It is about a 5-10-minute walk from Wengen station. Here are the directions:
From the station, head left up the main street lined with shops and hotels (Dorfstrasse), past the Hotel Silberhorn on the right, Männlichen cable car on the right, Hotel Bernerhof on the left, and uphill a bit past the Hotel Schönegg on the right and a chemist on the left. At the top of the hill, you will see a path on the left leading to the Swiss Protestant Church, where there is a lookout and seats. I have attached a map and a photo showing the view.
Most mountain transport in the Jungfrau Region, including the train to Wengen (or Grindelwald) and the Jungfraujoch, cable cars/train to Mürren and the cable car to the Schilthorn will be operating while you are there. The following are likely to be closed:
- Schynige Platte train (probably closed until 25 May 2018)
- Wengen-Männlichen cable car (probably closed 3 Apr-18 May 2018)
- Grindelwald Grund-Männlichen gondola (probably closed 3 Apr-18 May 2018)
- Mürren-Allmendhubel funicular (probably closed 9 Apr–22 Jun 2018)
>> Thursday may 17 to Zermatt
If you travel via the Lötschberg-Basistunnel (the fastest route, which the timetable will bring up by default), it will take up to 2 hours 48 minutes. However, by taking the tunnel, you miss out on the scenery.
To take a more scenic route, put "Kandersteg" in the "via" field of the online timetable. That journey will take you an hour longer, but the mountain scenery is lovely.
You can use the Swiss Timetable to plan a trip at your preferred time once the new timetable is released in mid-October.
>> Friday may 18 Zermatt
With only one day, you run the risk of the Matterhorn being in the clouds the whole time you are there, but the mountain transport will be running.
If you get there early enough on 17 May, and the weather is clear, it might be worth putting your luggage in the lockers at Zermatt station and going straight up to the Gornergrat, unless clear weather is also forecast for the following day. You can use the Swiss Timetable to work out what is feasible time-wise.
>> Saturday may 19 glacier express to Chur
In case you don't already know: reservations are compulsory on the Glacier Express.
It's probably a good idea to just go as far as Chur instead of continuing to St Moritz. That will cut a substantial amount of time from your long trip to Passau the following day. Furthermore, staying only one night in St Moritz is not really enough to enjoy what it has to offer in any case; and May is not a good time to visit St Moritz, because all the mountain transport except the Diavolezza cable car will be closed for maintenance. A lot of shops will be closed as well.
>> Sunday may 20th train to Passau
Just be aware that some options presented in the timetable include a sector by bus, so if you want to go the whole way by train, make sure not to pick a departure that involves one or more sectors by bus along the way.