How can I create a JQL Filter for this Requirement; It is possible to see who is in a project & when (including new starters as well as those who are in a project for a longer time)
You can't use JQL to search for user and membership. JQL is to find issues and only those!
You should be able to collect the membership information from the database (on Data Center) or the REST API.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.