[kevan]

In a similar vein, in the early days of launching Relay[1] I ended up spending a couple weeks in total squashing timestamp bugs. We were integrating with a few existing systems that used epoch seconds or milliseconds for timestamps and they usually didn't have a hint in the field name to tell what it was so it was really easy to miss in code reviews.

Our problems were caused by a mix of serialization format (JSON numbers) and not always converting into the language's date/time types at the boundary (sometimes raw epoch seconds/millis were passed around layers of code and only parsed into a date for display. That created opportunities for misinterpretation at every function call.

My general rules for non-performance critical code are

1. Always Parse into a first-class date/time/duration type at the serialization boundary.

2. Always use an unambiguous format (e.g. ISO-8601) for serialization

It's not the most efficient but lets you rely on the type system for everything in your code and only deal with conversion at one place.

[1] https://relay.amazon.com/