// (A)
time.AfterFunc(5 * time.Minute, func() {
    fmt.Printf("expired")
}
// (B) create a Timer object
timer := time.NewTimer(5 * time.Minute)
-timer.C
fmt.Printf("expired")
// (C) time.After() returns timer.C internally
-time.After(5 * time.Minute)
fmt.Printf("expired")