I saw that article too but reading man tcp(4) [1], it says that this value is in seconds for macOS and testing appears to confirm this. 

Where the unit of time is different, however, is with the old and new Windows keepalive options discussed in #32394. The SIO_KEEPALIVE_VALS set via the WinSock ioctl is in milliseconds [2] whereas the newer TCP_KEEP* flags are set in seconds [3] but this doesn't seem too bad as they are different interfaces. 

I'll add the tcp_keepalive flag to the same win_runtime_flags structure as the other options with minimum version 1709 and update the failing test accordingly to take account of the new option. 


[1] https://github.com/apple/darwin-xnu/blob/xnu-4570.1.46/bsd/man/man4/tcp.4#L172
[2] https://msdn.microsoft.com/en-us/library/windows/desktop/dd877220(v=vs.85).aspx
[3] https://docs.microsoft.com/en-us/windows/desktop/winsock/ipproto-tcp-socket-options