> the most reliable way is to represent them as fractions (x.as_integer_ratio() or (x.numerator, x.denominator))

I don't think that we can rely on non-dunder names like that. They are not reserved names, so classes can give them any semantics that they like. This is not just hypothetical: SageMath for example uses numerator() and denominator() methods, not properties.

If you really want to go through with this, probably a special method like __as_integer_ratio__ should be defined.

Anyway, I personally consider the double rounding for time.sleep() a non-issue. We are not trying to write a precise math library here, nobody will complain about sleeping a femtosecond too long.