- Content access by time
Content is free for a special time: f.e. the first 2 days after publishing or after 14 days

That's doable using CB Paid Subscriptions substitutions and its Joomla system plugin. See the below for example.

www.joomlapolis.com/news/18550-cbsubs-gpl-4-1-with-timed-content-taxes-inclusive-price-display-and-plan-substitutions-usable-anywhere

There's also an older solution that combines a few plugins below that still works.

www.joomlapolis.com/documentation/283-cb-paid-subscriptions/tutorials/18240-time-released-subscription-content-solution

Our CB Content Module also has a tab for timed content allowing the module to show/hide content based off a schedule.

- Content access by number of articles
A plan with a number of articles you can read per month/week, f.e. a test period: you have 3 articles free

There's no functionality for that. Doubt there are plans for it either as it requires read tracking every article for every user. It's doable using CB Auto Actions and a custom database table, but it'd be a lot of work.

- Content access by custom field
I have a custom field called 'exclusive'. All articles with this entry should have paid access.

That's doable using CB Content Bot and using IF substitutions inside your article. See the below regarding substitution usage.

www.joomlapolis.com/documentation/279-community-builder/tutorials/18353-using-substitutions-throughout-cb

1. Content access by time
What I mean is the time the article is published. F.e. the first 7 days after publishing the article is only to read full for members (the other can only read the introtext), after the 7 days the article is free for everyone.
Your examples mean only the time of the subscription.
AND: I have to put a plugin-string in every article? It would be much more comfortable to set the condition in the content tab of the plan.
May be it is possible - but I don't understand it....

Sounds like your timed content has nothing to do with CBSubs then. We don't have a general timed content usage like that. The only thing like that available is the timed content feature in CB Content Module, but that's for showing/hiding the module. You'd need to look into 3rd party solutions for this since you don't want it to be based off a subscription.

2. Content by custom field
What I mean is a custom field in the article. If any article has the custom field with the value "plus", this article should only to read full by members. All the other users could only read the introduction.
Is this possible?

You can substitute fields into a Joomla article using the CB Content Bot. Once installed and publish you can use the substitutions shown in the below tutorial in your articles. Aside from that I don't understand what you're asking, sorry.

www.joomlapolis.com/documentation/279-community-builder/tutorials/18353-using-substitutions-throughout-cb

What I want to do is the same as many magazines and newspapers doing: some articles are only accessible for members. All guests can see the introduction. These articles are from different categories, so the category is not the right way to protect the content. I need any other criterion. My idea is to take a content cutom field, because I can show it in the frontend like "for members" or similar.

Ah, I understand now. Yes that's very doable. You'll need to be sure you're using the "read more" feature built into Joomla articles. Next you need to protect Joomla articles or their categories within your plans under Integrations > Content, which is provided by CBSubs Content. Now within CBSubs > Settings > Integrations > Content/Extensions ensure "Still show intro text for articles" is set to "Yes: articles introductions remain always visible" or "Depends: articles introductions are visible only if there is also a "read more" main text". This should allow anyone to read the intro text, but the actual article is restricted to a subscription.

This protection should only run for a special time, f.e. one week. After that the content is free accessible.

This would be the difficult part. There is no timing functionality for this feature. You would have to manually edit your plans and remove those articles or categories from CBSubs Content protection.

And of course I dont want to change my content every day, it should be run automaticly.

We don't have any functionality for that. Our timed content functionality only works with subscription dates so it could only do something like show X if subscribed for Y days, etc.. Have added a feature ticket to see if this is something we can support in a future release.

forge.joomlapolis.com/issues/7924