I got my first Scoby from a Russian friend years ago.
He said I can also use it as a facial pack.
Actually I have never tried it, but it seems to be a good idea.
When we moved I didn’t wrap up my Scobies very well and then I forgot about them a few days.
That’s the reason I stopped, because they were not active anymore.
With every batch You will have a new Scoby, after a while it will get so thick that You have to throw them out.
Or use them or give them away of course.
Here is the website where I found the recipe. There is also much more information.
You can try the Kombucha to see if it is ready. Is it too sweet it needs longer.
It really depends on how much sugar You use. The more sugar, the longer time it takes.
I would just go by taste and not the number of days.