I disagree that 5e3 is clever. Exponential notation is something that every coder should learn. It appears in a lot of places and is much clearer that expanded numbers.
I did a lot of work with nanoseconds much, and I would have to see 1500000000 in the code versus 1.5e9. With larger numbers the exponential format is preferred.
Of course, I'd also like a language that allows separators (I did in Leaf, like 5_000.
Note though, on the second I think any api that accepts something other than seconds for duration by default is broken. Seconds is the natural time, milliseconds is unusual. Thus a conversion function would be nice to see there.
It's clever in that scenario because seeing the exponential notation for most people will require more brain processing power than simply seeing 5000 milliseconds or 5 seconds.
It also really just depends on what you're building. Web development rarely requires you to use exponential notation, and so declaring it as "something that every coder should learn" is not an absolute that I can get behind.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.