Hello everyone,
My authorization to move in to Switzerland came out on May 26 and states that its validity is till August 25 and it serves me for 1 year.

I have taken my passport today to the Swiss embassy in my country to get my D- D-type visa.

My question is as follows:
Should I be in Switzerland before 25 August? Or does the 3 months period begin after my passport is stamped? And if so, how long would I have to stay there before being able to come back to my country to proceed with the wedding celebrations with my husband?

Your D visa will most likely be valid until Aug 25, so you need to first enter Switzerland before that date (but it's fine if you enter on the last day).
You must register at your commune and apply for a residence permit in two weeks after entering CH I think.
Then you're free to go but if your nationality needs a visa to enter Schengen you'll need to apply for and get a return visa at the OCP to be able to come back after Aug 25 (or wait till you get your permit but that can take months in Geneva).

Thank you for your reply.

However, the “duree de validite du visa” section in the authorization document is empty. The “authorization valable jusqu’au” section states August 25, which I interpreted as the last date the Swiss authorities give permission to the Swiss Embassy here to give me a visa.

When my husband contacted the person responsible for this in Switzerland, she told him that the visa would be valid for 90 days after I hand in my passport. But the collaborator today at the embassy told me the opposite, which is why I am so concerned about this.

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.

Update: the embassy confirmed that it will be valid till August 25. They will contact the OCP to request a slight extension till the 29th.

My question is:
If the OCP denies this request, will the visa be still given to the 25th?

Yes. The fact you requested a change to the 29th doesn't mean they'll magically revoke the 25th and put something else like the 16th just to be mean.

Haha thank you for putting my mind at ease!