This would allow formatting date times with the typical tokens like `%Y-%m-%d`. Chrono supports this, and its support should be used as a template for the Hifitime implementation: https://docs.rs/chrono/latest/chrono/format/index.html , https://docs.rs/chrono/latest/chrono/format/strftime/index.html . Time-rs also has extensive support for formatting: https://time-rs.github.io/book/api/well-known-format-descriptions.html .