Hello,
I think I had the same situation. The date in the visa printed in the passport is the last date to enter Switzerland and it's valid only once. As long as the stamp you get at the airport is before this date you'll be fine. Then you request the residence permit in Genève in the commune where you will live, but getting the permit card may take 3 or more months.
You'd be wondering how to travel outside Switzerland after your first visa expired by Aug 25. The answer is another temp visa printed in your passport called
visa de retour. You have to request it at the control de population/office de population in Genève.
https://www.ge.ch/obtenir-visa-retou...sa/visa-retour
While living in Neuchâtel I had to ask for visa de retour several 2 or 3 times. Since I had to request permit renewal every year, I had no permit card during 4-5 months every year.