dispatch_time(3) on macOS

The text 07414c66db2d, as macOS 10.13.6, macOS 10.13.5, macOS 10.13.4, macOS 10.13.3, macOS 10.13.2, macOS 10.13.1, macOS 10.13 shipped it.

Calculate temporal milestones

dispatch_time(3) on macOS now