diff --git a/index.php b/index.php
index 2863698..e84ee26 100644
--- a/index.php
+++ b/index.php
@@ -599,7 +599,13 @@ if ($_SERVER['REQUEST_METHOD'] == "POST") {
             let dt = new Date(s)
             dt.setMinutes(dt.getMinutes() + parseInt(d))
 
-            document.getElementById(end).value = dt.toISOString().slice(0, 16)
+            let yyyy = dt.getFullYear()
+            let mm = String(dt.getMonth() + 1).padStart(2, '0')
+            let dd = String(dt.getDate()).padStart(2, '0')
+            let hh = String(dt.getHours()).padStart(2, '0')
+            let mi = String(dt.getMinutes()).padStart(2, '0')
+
+            document.getElementById(end).value = `${yyyy}-${mm}-${dd}T${hh}:${mi}`
 
         }