dispatch_time(3) on macOS

The text 4e58f5270666, as Mac OS X 10.8.5, Mac OS X 10.8.4, Mac OS X 10.8.3, Mac OS X 10.8.2, Mac OS X 10.8.1, Mac OS X 10.8 shipped it.

Calculate temporal milestones

dispatch_time(3) on macOS now