It's surprising to me that there are such various levels of coarseness each browser vendor chose:

Gecko [0]: accurate to 20us

Edge [1]: accurate to 20us, with an additional 20us of noise

Chrome [2]: accurate to 100us (thanks mkeblx for finding this)

Safari [OP]: accurate to 1000us

[0] https://blog.mozilla.org/security/2018/01/03/mitigations-lan...

[1] https://blogs.windows.com/msedgedev/2018/01/03/speculative-e...

[2] https://chromium-review.googlesource.com/c/chromium/src/+/85...