fix: human-readable timestamp of sent newsletters

includes/class-newspack-newsletters.php

@@ -546,8 +546,6 @@ public static function display_post_states( $post_states, $post ) {
 
 		$post_status = get_post_status_object( $post->post_status );
 		$sent        = self::is_newsletter_sent( $post->ID );
-		$is_public   = get_post_meta( $post->ID, 'is_public', true );
-
 		if ( $sent ) {
 			$time_diff = time() - $sent;
 
@@ -1176,17 +1174,17 @@ public static function is_newsletter_sent( $post_id ) {
 		}
 
 		/** Detect meta that determines the sent state */
-		$sent = get_post_meta( $post_id, 'newsletter_sent', true );
-		if ( 0 < $sent ) {
+		$sent         = get_post_meta( $post_id, 'newsletter_sent', true );
+		$is_published = 'publish' === get_post_status( $post_id );
+		$publish_date = $is_published ? get_post_datetime( $post_id, 'date', 'gmt' )->getTimestamp() : 0;
+		if ( 0 < $sent && $sent === $publish_date ) {
 			return $sent;
 		}
 
 		/** Legacy check for sent/publish newsletters without meta. */
-		if ( 'publish' === get_post_status( $post_id ) ) {
-			$post = get_post( $post_id );
-			$sent = strtotime( $post->post_date );
-			self::set_newsletter_sent( $post_id, $sent );
-			return $sent;
+		if ( $publish_date ) {
+			self::set_newsletter_sent( $post_id, $publish_date );
+			return $publish_date;
 		}
 
 		return false;