Is it possible to create notifications on webcontent which should configurable as a model and fragments and should be dismissable after sometime

@rengan76 : It's possible to create the experience that you have described in your question.

There is no OOB solution to showcase any header alerts .You would have to write your own logic to implement that. Here is the high level solution that how I have implemented in it my project.

1. Create a experience fragment to showcase the header section.

2. Include this experience fragment in the DOM elements at the top of the base page. Provide the flexibility in the page properties in case the business doesn't want to show header alert for any set of the pages. This header alert would be inheritable so that when it's implemented on the Parent page or home page, this header would be displayed at the entire hierarchy of the content. 

3. Implement the logic in the JavaScript to show and hide this header section based on the duration of the time.

If you are talking about some alert Pop-ups on the header, yes that is possible to implement with custom implementation.

1. Create a configuration fragment or fragments with your alert messages

2. Configure the the fragment path in your root page properties and also checkbox if you want to toggle the alert in different pages

3. You should already have static Javascript and css code which shows the alert, integrate same based on the above configurations and it should show the alerts based on the configurations in the page.