I already thought you would not have so much time. But let me warn you, once you've seen the Lauterbrunnen area you might want to come back ;-).
I don’t know if it’s safe to start at 10:36 am, leaving Geneva Airport by train, when you arrive at 10:00. In this case you would arrive in Lauterbrunnen after a 4 hours train ride, at 14:25 (through Bern and Interlaken Ost). Checking out, going to the railway station etc. might take some time. The next possibility for you is leaving at 11:01 and then too you will arrive in Lauterbrunnen at 14:25 pm.
The train ride between Lauterbrunnen and Locarno will take you about 4 to 5,5 hours (depending on your choice). If you want to arrive at 23:30 in Locarno, you might leave Lauterbrunnen at either:
- 16:33 (via Interlaken Ost, Lucerne, Art Goldau and Bellinzona, arriving in Locarno at 21:57). In this case you will take the beautiful track through the Brünig Pass by daylight, or
- 18:03 (via Interlaken Ost, Spiez and Domodossola, arriving in Locarno at 22:08).
In my view the train ride between Domodossola and Locarno (the Centovalli Railway track) is too impressive to take when it's getting dark, so my suggestion would be, leave Lauterbrunnen at 16:33.
About two hours is enough to give you a first impression of the Lauterbrunnen area (correction: of course it's not enough :-)). Leaving the train station of Lauterbrunnen, turn left and go towards the beautiful Staubachfall (waterfall), you can't miss it, and do with your time as you please.
I am quite sure there are luggage lockers at Lauterbrunnen railway station.
A rough calculation of costs of train rides from Geneva airport via Lauterbrunnen to Locarno and from there back to Geneva airport adds up to about CHF 276.
It would probably be best if you purchase a Swiss Half Fare Card, which you can order online
(CHF 99 and giving you 50 % discount at your trips).
Please check everything for yourself at Timetable Switzerland
, just to make sure.
I hope this helps and I whish you a very pleasant stay in Switzerland!