diff --git a/modules/course_signup/course_signup.module b/modules/course_signup/course_signup.module
index da9c1bb..939608a 100644
--- a/modules/course_signup/course_signup.module
+++ b/modules/course_signup/course_signup.module
@@ -254,10 +254,9 @@ function course_signup_course_access($op, $node, $user) {
           $items = field_get_items('node', $node, $field['field_name']);
           if (!empty($items[0]['value'])) {
             // This node is signup-enabled and closed by date.
-            $date = new DateTime($items[0]['value'], new DateTimeZone('UTC'));
+            $close_stamp = strtotime($items[0]['value'] . ' UTC');
             $signup_close_early = variable_get('signup_close_early', 0);
-            $date->sub(date_interval_create_from_date_string("$signup_close_early hours"));
-            $close_stamp = $date->getTimestamp();
+            $close_stamp -= ($signup_close_early * 60);
             if (REQUEST_TIME > $close_stamp) {
               $hooks['course_signup'] = array(
                 'header' => t(''),