This not only solves the warning/error brought up during compilation, it's also just a sort of belt'n'braces approach to make absolutely sure the timestamp length is correct and didn't get truncated or some other error. This was a new warning/error introduced back in gcc 7.1, and it's one of those "you *should* do it this way because it's technically the correct way" things that most developers roll their eyes at but, logically, they're technically correct.
