public GracefulShutdownBuilder quietPeriod(Duration quietPeriod) {
        requireNonNull(quietPeriod, "quietPeriod");
        this.quietPeriod = validateNonNegative(quietPeriod, "quietPeriod");
        return this;
    }
Sets the quiet period to wait for active requests to go end before shutting down.
{@link Duration#ZERO} means the server will stop right away without waiting.

<p>The default is {@link Duration#ZERO}.
core/src/main/java/com/linecorp/armeria/server/GracefulShutdownBuilder.java