It is easy to set comment expiration date on per post/post type basis in WordPress. Comment Expirator plugin enables you to close comments, pingbacks and also trackbacks on your posts, pages and custom post types on an individual basis.
This way you can set a custom date and time for deactivating comments for each and every article you write on your website.
How To Use Comment Expirator Plugin?
Install and activate it. After activation visit your admin area dashboard Settings -> Comment Expirator and tick the post type where you like displaying comment expiration options.
This adds a new metabox on ADD NEW/EDIt content screens from where you can set a deactivation date & time for comments and chose if trackbacks and pingbacks should also be closed at the same time.