Resolve #3419851 "Officehoursdatehelperformat causes fatal"

Closes #3419851

src/OfficeHoursDateHelper.php

@@ -184,7 +184,7 @@ class OfficeHoursDateHelper extends DateHelper {
       return NULL;
     }
 
-    if ($time > 2400) {
+    if (is_numeric($time) && ($time > 2400)) {
       // if (OfficeHoursDateHelper::isExceptionDay($day)) {
       // A Unix datetimestamp.
       switch ($time_format) {