Timestamp inside clientlibs.min.css

I would strongly recommend this: Versioned ClientLibs

I meant to say Instead of running replace token plugin You can run java executable plugin in maven build and read your js and css file in that java program and append timestamp in css and js file using java code.

Thats fine but I need the value in js and css file , not in Java file

yes, you can get timestamp in maven  Stamping Version Number and Build Time in a Properties File with Maven - DZone Java

You can try to execute a java program in maven build phase and try to do normal file read and write with replace token.

3 ways to run Java main from Maven | Vineet Manohar's blog

Is there a way we can read maven timestamp value inside js and css files.

In JSP we can do as per below link

How to display maven project version in your webapp | Vineet Manohar's blog

But same doesn't work for js and css as replace <token>PROJECT_VERSION</token> happens for JSP file only.

Have you looked at Versioned ClientLibs?

Versioned ClientLibs

So is there a way to check that clientlibs added to the page is of latest build and not cached?

As we include clientlibs using categories and page source have something like this

/etc/clientlibs/clientlibs.min.css

So how can we check if its of latest build or old build

There is no AEM specific functionality that will let you do this. To get a time stamp into a JS or CSS, you need to add custom app logic.

html - How to append timestamp to the javascript file in <script> tag url to avoid caching - Stack Overflow