Hello Konstantin Babich
I suggest you to look up the train schedule on sbb.ch/en.
To do First and Geneva on the same day? Impossible.
Keep in mind that you will go to a higher altitude, which can make you tired as you are not used to it. Also, I have read in one of your replies that you will travel with your mother? My mother is in her seventies and absolutely fit, but she would definitely insist when I plan to travel from Prague to Grindelwald - First- Grindelwald - Geneva - Grindelwald all in one day.
Grindelwald to Geneva is 3h31 mins one way. And I can tell you, Geneva is not worth that detour.
If you want to stop in a medieval city, why don’t you stop in Bern on the way to Grindelwald? Or, why don’t you stop in Lucerne which is very scenic and a must to see?
You can buy the Swiss Travel Pass online at any time, it is issued and e-mailed to you instantly, within seconds.
Kind regards,
Roland