private static long toMillis(long micro) {
        if (micro >= 0) {
            return TimeUnit.MICROSECONDS.toMillis(micro);
        }
        return -1;
    }
Returns the duration which was taken to wait for the completion of an existing connection attempt
in order to use one connection for HTTP/2.

@return the duration, or {@code -1} if there was no action to get a pending connection.
core/src/main/java/com/linecorp/armeria/common/logging/ClientConnectionTimings.java