public void setPreferredMaintenanceWindow(String preferredMaintenanceWindow) {
        this.preferredMaintenanceWindow = 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, then changing this parameter will cause a reboot of the DB
instance. If 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 pending changes are applied.
</p>
<p>
Default: Uses existing setting
</p>
<p>
Format: ddd:hh24:mi-ddd:hh24:mi
</p>
<p>
Valid Days: Mon | Tue | Wed | Thu | Fri | Sat | Sun
</p>
<p>
Constraints: Must be at least 30 minutes
</p>

@param preferredMaintenanceWindow
       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, then changing this parameter will cause a
       reboot of the DB instance. If 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 pending changes are applied.</p>
       <p>
       Default: Uses existing setting
       </p>
       <p>
       Format: ddd:hh24:mi-ddd:hh24:mi
       </p>
       <p>
       Valid Days: Mon | Tue | Wed | Thu | Fri | Sat | Sun
       </p>
       <p>
       Constraints: Must be at least 30 minutes
aws-java-sdk-neptune/src/main/java/com/amazonaws/services/neptune/model/ModifyDBInstanceRequest.java