I am a non-EU/non-Swiss national living in the UK. I will get married to my fiance (who holds a B permit in CH) in Switzerland, and intend to move there. So, I will travel to CH for marriage with a D type visa. As far as I know, if everything goes fine, I am eligible to obtain a residence permit through my partner with this visa. The only problem is that I plan to completely move to Switzerland not immediately after the wedding but 4-5 months after the start date of the visa due to some things I need to wrap up in the UK. Does anyone know if it would be a problem to have a residence permit in both CH & UK during this period, and move to CH later on? Any experience?
Once you get that D visa, you have a limited time to move to Switzerland. It will take a bit of time to get your residence permit issued (which you have to be here for, fingerprint and photo etc). Without the permit, you will need to pay for another document to leave and enter CH. Once you have that D visa and permit, you can't spend more than 6 in 12 months outside of Switzerland or you lose it.
You also have this the wrong way around. Your partner needs to apply for a fiancé/fiancée permit for you to come over to help with the wedding preparations. If that is granted you’ll get a Type D visa which will allow you to enter the country during a specified period as Island Monkey said. Since the permit will already be approved (as your partner has to prove they have suitable accommodation for both of you and can also support you financially) getting the biometric part done shouldn’t take too long. You won’t be able to get married and then go straight back to the UK because of needing to do the biometrics. As Island Monkey said there is a document you can get if you can’t wait for the permit to arrive, but even so you still need to be here long enough to do the biometric side of things.
The Type D visa is only to allow you to enter the country for more than the 90 day tourist limit; it’s the residence permit that allows you to live and maybe work here. And the visa will not be issued to you without a permit having been pre-approved.
The long term visa gonna be valid for 3 months. if you apply for a multi entry one you can go out and in switzerland within the validity of your visa but need to be back to CH before it's expired. If you move to Zürich area you'll need to expect 6-8 weeks to get an appointement for the biometrics.
Finally if you hold a schengen visa you could travel after your CH long term visa is expired but you may be asked for some explanations at the border.
You can also ask for a "return visa" but you'll need to justify why you need to travel and can't wait to get your residence permit first
Get your B permit quick, deregister in the UK (no idea how that works) and register in CH. Then, you can spend up to 6 months abroad (CH regulation on your B permit), that should do.
If you return regularly, like at least every fortnight, that might even be permanently possible, but in such a case you should enquire with your commone beforehand to make sure.
Also, you may want to enquire what both tax offices think about that, in particular if the UK deems you tax resident or not during that time. CH certainly will, after all you're registered.
I'm not completely sure that the OP is British. If they are not, there could be a residence visa that needs cancelling. Also you have to cancel your Council tax, which is kind of like de-registering.
I was assuming UK citizenship. I don't think it would be a problem, assuming OP's staying there makes sense from a 3rd-party perspective. Like unwinding a larger business, finishing a project, etc.
But people are right with pointing out that OP may not be british (seems not to be, what Island Monkey quotes pretty much says OP isn't). That may have things look different, which brings the risk that the marriage gets de-recognised, a risk not worth taking. Coordinating with the authorities seems a must (wouldn't hurt with UK citizenship either for that matter), see what they say.