if you use other Async runtimes, you need to "wire them up", in this case by providing a "sleep" implementation. I'd strongly recommend using Tokio, especially if you're a beginner. I think the "beefy" statements are not necessarily accurate. You can use it as a single-threaded runtime if you want. Tokio is not going to have a significant impact on your compile times or binary size (given you're already using the SDK!)