Use a different image on the single announcement page, than what is used on the timeline.

custom-interior-image-timeline-express.php

/**
 * Timeline Express Add Custom Metabox
 * @param array $options Array of options for Timeline Express.
 */
function define_custom_excerpt_metabox( $options ) {
    $announcement_custom_metabox = new_cmb2_box( array(
       'id' => 'custom_meta',
       'title' => __( 'Additional Announcement Meta', 'text-domain' ),
       'object_types' => array( 'te_announcements' ), // Post type
       'context' => 'advanced',
       'priority' => 'high',
       'show_names' => true, // Show field names on the left
    ) );
    // Container class
    $announcement_custom_metabox->add_field( array(
       'name' => __( 'Single Featured Image', 'text-domain' ),
       'desc' => __( 'This is the image used on the single announcement page.', 'text-domain' ),
       'id' => 'announcement_single_image',
       'type' => 'file',
    ) );
}
add_action( 'timeline_express_metaboxes', 'define_custom_excerpt_metabox' );

/**
 *	Hook in and display our new featured image (if set) above the content
 *	- Timeline Express Single Announcement Images
 */
function replace_default_timeline_express_single_image( $image, $post_id ) {
	$post = get_post( $post_id );
    if ( is_single() && timeline_express_get_custom_meta( $post_id, 'announcement_single_image', true ) ) {
       return wp_get_attachment_image(
			get_post_meta( $post_id, 'announcement_single_image_id', true ),
			'medium',
			false,
			array(
				'title' => get_the_title( $post ),
				'class' => 'announcement-banner-image',
				'style' => 'width: auto',
			)
		);
    } else {
       return $image;
    }
}
add_filter( 'timeline_express_image', 'replace_default_timeline_express_single_image', 10, 2 );