How to disable edit post option 12 hours after post publication for contributors?

The other suggestions (and the accepted answer in your link) temporarily change a user’s capabilities globally. That is a hack. There is hook specifically designed for conditionally adjusting capabilities for specific content: map_meta_cap.

When WordPress checks whether a user can edit a post, it checks if the user can edit_post. WordPress decides which actual capability users have that this maps to using the map_meta_cap() function.

For example, when checking if a user can edit a post, it checks if the post was authored by the current user. If it was, then it maps the ‘meta capability’ edit_post to the ‘primitive capability’ edit_posts. If the post was authored by someone else it maps it to edit_others_posts. Then it checks if the current user has the mapped capability.

So we can hook into this process so that whenever WordPress maps edit_post we will check if the current user is a Contributor, and if the post is older than 12 hours. If both those things are true we will map edit_post to do_not_allow, meaning that the user will not be allowed to edit it:

function wpse_319901_contributor_can_edit( $caps, $cap, $user_id, $args ) {
    // Stop if this isn't a check for edit_post or delete_post.
    if ( $cap !== 'edit_post' || $cap !== 'delete_post' ) {
        return $caps;
    }

    // Get the current user's roles.
    $user  = get_userdata( $user_id );
    $roles = $user->roles;

    // Stop if the user is not a Contributor.
    if ( ! in_array( 'contributor', $roles ) ) {
        return $caps;
    }

    // For edit_post the post ID will be the first argument in $args.
    $post = get_post( $args[0] );

    // Is the post older than 12 hours?
    if ( get_the_time( 'U', $post ) < strtotime( '-12 hours' ) ) {
        // If so, do not allow the user to edit it.
        $caps[] = 'do_not_allow';
    }

    return $caps;
}
add_filter( 'map_meta_cap', 'wpse_319901_contributor_can_edit', 10, 4 );

You can read more about capabilities and how meta capabilities are mapped to primitive capabilities here.