diff --git a/timehelper/go.mod b/timehelper/go.mod
new file mode 100644
index 0000000..fa66582
--- /dev/null
+++ b/timehelper/go.mod
@@ -0,0 +1,3 @@
+module git.blauwelle.com/go/crate/timehelper
+
+go 1.20
diff --git a/timehelper/time.go b/timehelper/time.go
new file mode 100644
index 0000000..b1419b3
--- /dev/null
+++ b/timehelper/time.go
@@ -0,0 +1,8 @@
+package timehelper
+
+import "time"
+
+// SetupCST 把本地时区固定到CST
+func SetupCST() {
+	time.Local = time.FixedZone("CST", 8*3600)
+}
diff --git a/timehelper/time_test.go b/timehelper/time_test.go
new file mode 100644
index 0000000..a70c65c
--- /dev/null
+++ b/timehelper/time_test.go
@@ -0,0 +1,34 @@
+package timehelper_test
+
+import (
+	"fmt"
+	"time"
+)
+
+// Javascript 只能精确到毫秒:
+// new Date('2023-01-15T15:16:17.123456789+08:00').toISOString()
+// Output: '2023-01-15T07:16:17.123Z'
+func ExampleRFC3339Nano() {
+	t, _ := time.Parse(time.RFC3339Nano, "2023-01-15T15:16:17.123456789+08:00")
+	fmt.Println(t.Format(time.RFC3339Nano))
+	// Output: 2023-01-15T15:16:17.123456789+08:00
+}
+
+func ExampleRFC3339Nano2Sec() {
+	t, _ := time.Parse(time.RFC3339Nano, "2023-01-15T15:16:17.123456789+08:00")
+	fmt.Println(t.Format(time.RFC3339))
+	// Output: 2023-01-15T15:16:17+08:00
+}
+
+// 使用 RFC3339 没有丢失纳秒精度
+func ExampleRFC3339Sec2Nano() {
+	t, _ := time.Parse(time.RFC3339, "2023-01-15T15:16:17.123456789+08:00")
+	fmt.Println(t.Format(time.RFC3339Nano))
+	// Output: 2023-01-15T15:16:17.123456789+08:00
+}
+
+func ExampleRFC3339NanoOtherZone() {
+	t, _ := time.Parse(time.RFC3339Nano, "2023-01-15T15:16:17.123456789+09:00")
+	fmt.Println(t.Format(time.RFC3339Nano))
+	// Output: 2023-01-15T15:16:17.123456789+09:00
+}