I installed pay plugin just to test it and I see it doesn't say anywhere when the listing is premium till which date it is premium or highlighted etc.Can this be added?

Also even when listing is premium when I enter the listing it show me again to make it premium even if is already premium 7 days so let say I add it again 30 days premium will the premium be extended for 30 or 30 + previous 7 = 37?

@nutriblr
Plugin shows this information in tooltip to the user.
You can test your another question by yourself, but yes if there is already active premium label, it will be extended.