This is just best effort on google's end right? Don't think anything is documented/guaranteed such that you would be able to, for ex. rely on it like spanner's use of true time.
Sure, you'd have to invent the rest, but TrueTime isn't about having perfect clocks, it's about estimating the error of your peer's clocks. Having a reasonable platform clock is a good starting point, and addresses the problems discussed in the Jane Street article.