Don't show timezone if it's an "all day" event

.gitignore

@@ -18,6 +18,7 @@ mu-plugins/*
 !mu-plugins/mu-autoloader.php
 !mu-plugins/osi-event-list
 !mu-plugins/osi-sponsors-list
+!mu-plugins/osi-events-manager-tweaks
 
 themes/*
 !themes/osi

mu-plugins/osi-events-manager-tweaks/osi-events-manager-tweaks.php

@@ -0,0 +1,19 @@
+<?php
+/**
+ * Plugin Name: OSI Events Manager Tweaks
+ * Description: Customizations for the Events Manager plugin.
+ * Version: 1.0.0
+ * Author: WordPress.com Special Projects
+ * Author URI: https://wpspecialprojects.wordpress.com/
+ */
+
+add_filter('em_event_output_placeholder', 'osi_em_event_output_placeholder', 10, 5);
+function osi_em_event_output_placeholder( $replace, $EM_Event, $full_result, $target, $placeholder_atts ) {
+	if ( '#_EVENTTIMEZONE' === $full_result ) {
+		$event_times = $EM_Event->output('#_EVENTTIMES');
+		if ( 'All Day' === $event_times ) {
+			$replace = '';
+		}
+	}
+	return $replace;
+}