OK, I did "for i in {1..10}; do o//examples/rusage.com o//examples/hello.com; done" and the lowest wall time I got was 1,140us, which is a lot more than your 90us for some reason. There's probably something wrong with my setup. Maybe it takes my machine that long to come out of some P-state or C-state sleep mode I don't understand.

Then for my musl-gcc hello world, I did, "for i in {1..10}; do o//examples/rusage.com ../hello" and the lowest wall time I got was 120us. But most of the runs were closer to 350us.

So, my attempt to answer your, "Why does hello world take 1.8ms to run?" question is: a) they timed it with "time" which measures lots of overhead, b) there's something wrong with their setup that means they are mostly timing the time taken for a CPU core to wake up.