io-layer only has 1s resolution for file time information.
This is (somewhat) problematic because e.g. the Microsoft/msbuild unit tests sleep for 100ms between creating files, expecting the file times to differ. Under mono, the file times don't differ, because io-layer uses the 1s-resolution `struct stat` members, not the 1ns members:
In order to get 1ns resolution, the `struct stat::st_mtimespec` and other `struct stat::st_*timespec` fields should be used instead of the `struct stat::st_*time` members.
The st_mtimespec.tv_nsec field seems to be 0 under osx, so it still cannot give sub second accuracy.
Indeed, wikipedia mentions that HFS+ only supports 1s date resolution:
At least this should work on Linux...