public String getPreferredMaintenanceWindow() {
        return this.preferredMaintenanceWindow;
    }
<p>
The weekly time range (in UTC) during which system maintenance can occur, which might result in an outage.
Changing this parameter doesn't result in an outage except in the following situation, and the change is
asynchronously applied as soon as possible. If there are pending actions that cause a reboot, and the maintenance
window is changed to include the current time, changing this parameter causes a reboot of the instance. If you
are moving this window to the current time, there must be at least 30 minutes between the current time and end of
the window to ensure that pending changes are applied.
</p>
<p>
Default: Uses existing setting.
</p>
<p>
Format: <code>ddd:hh24:mi-ddd:hh24:mi</code>
</p>
<p>
Valid days: Mon, Tue, Wed, Thu, Fri, Sat, Sun
</p>
<p>
Constraints: Must be at least 30 minutes.
</p>

@return The weekly time range (in UTC) during which system maintenance can occur, which might result in an
        outage. Changing this parameter doesn't result in an outage except in the following situation, and the
        change is asynchronously applied as soon as possible. If there are pending actions that cause a reboot,
        and the maintenance window is changed to include the current time, changing this parameter causes a
        reboot of the instance. If you are moving this window to the current time, there must be at least 30
        minutes between the current time and end of the window to ensure that pending changes are applied.</p>
        <p>
        Default: Uses existing setting.
        </p>
        <p>
        Format: <code>ddd:hh24:mi-ddd:hh24:mi</code>
        </p>
        <p>
        Valid days: Mon, Tue, Wed, Thu, Fri, Sat, Sun
        </p>
        <p>
        Constraints: Must be at least 30 minutes.
aws-java-sdk-docdb/src/main/java/com/amazonaws/services/docdb/model/ModifyDBInstanceRequest.java