A long-time reader but first-time poster
The usual preface apology -- I've trawled through forum but cannot find the relevant info...

When the (first-time) B-Permit is issued -- is it dated from the day-of-application, the day-of-granting, or the day-of-issuance?

I am a U.K. citizen currently residing here under the E.U. 90day jobseekers rule, soon to receive a contract of employment, and obviously worried about the dreaded Brexit extension period deadline of 31.12.20 looming!
If I submit my residence permit application at my Gemeinde this month, how worried should I be about it not receiving it in time?

A huge thanks to all here who've already supplied great information and advice

The date you register as being resident here.

My first permit was dated the day I arrived, despite not completing the formalities for over 90 days after arrival. (Long boring story)

In some cantons the practice is to wait until the employment start date (i.e. the moment the EU person starts exercising freedom of movement rights) to issue the permit

My first post, after years of following the discussions here.

I am wondering whether having the Jobseeker’s permit itself means already exercised the EU freedom of movement rights. Assuming the permit is valid until through 31-Dec, say until 30-Jan, is that not enough to be able to continue exercising freedom of movement rights from 01-Jan? Or is having a proper L or B permit before 31-Dec the only way (for employment path)?

Thanks for the replies to all

An update:
I signed the employment agreement last week with start date in early December, and submitted it to the Gemeinde this week.
They inform me that I can work immediately, but may have to wait up to two months for issuance of the permit.
Waiting to see...

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Re. your query/(situation?) Monocle:
No idea! I searched for an answer to this question myself for a fallback in case I couldn't gain employment, but couldn't find any definite information either way.
As a last resort maybe it's worth a try (unless anyone knows otherwise)?!

For me in Basel it was "date of arrival in CH". Not sure what it would be for you but it surely would not be date of issuance or 'granting'. i.e. don't worry.

A further update:

I received the notification letter from the Gemeinde earlier this week, and have now collected my permit... a 5yr EU/EFTA B !!!

Its "Ausgestellt durch" date is early December, coincidentally(?) the same day as my employment contract's start date.
Whereas its "Einreisedatum" is the date I arrived and signed my rental contract, and subsequently registered my residence from -- back in September.
Both are before 31.12.2020 which is all that matters to me

Now time for a good few Feldschlösschens

Thanks again for everyones' advice!