val query :
[ `Error of Core.Exn.t | `Offset of Core.Time.Span.t | `Timeout ]
query hostnamereturns the difference between the clock on the local host and the clock on the host specified by
If the remote host is down or not running an (S)NTP service this
call will `Timeout. Other errors, including some classes of resolution
or network will raise an exception, which will be returned as `Error.