public void setScheduleAt(String scheduleAt) {
        this.scheduleAt = scheduleAt;
    }
<p>
When to start the service software update.
</p>
<ul>
<li>
<p>
<code>NOW</code> - Immediately schedules the update to happen in the current hour if there's capacity available.
</p>
</li>
<li>
<p>
<code>TIMESTAMP</code> - Lets you specify a custom date and time to apply the update. If you specify this value,
you must also provide a value for <code>DesiredStartTime</code>.
</p>
</li>
<li>
<p>
<code>OFF_PEAK_WINDOW</code> - Marks the update to be picked up during an upcoming off-peak window. There's no
guarantee that the update will happen during the next immediate window. Depending on capacity, it might happen in
subsequent days.
</p>
</li>
</ul>
<p>
Default: <code>NOW</code> if you don't specify a value for <code>DesiredStartTime</code>, and
<code>TIMESTAMP</code> if you do.
</p>

@param scheduleAt
       When to start the service software update.</p>
       <ul>
       <li>
       <p>
       <code>NOW</code> - Immediately schedules the update to happen in the current hour if there's capacity
       available.
       </p>
       </li>
       <li>
       <p>
       <code>TIMESTAMP</code> - Lets you specify a custom date and time to apply the update. If you specify this
       value, you must also provide a value for <code>DesiredStartTime</code>.
       </p>
       </li>
       <li>
       <p>
       <code>OFF_PEAK_WINDOW</code> - Marks the update to be picked up during an upcoming off-peak window.
       There's no guarantee that the update will happen during the next immediate window. Depending on capacity,
       it might happen in subsequent days.
       </p>
       </li>
       </ul>
       <p>
       Default: <code>NOW</code> if you don't specify a value for <code>DesiredStartTime</code>, and
       <code>TIMESTAMP</code> if you do.
@see ScheduleAt
aws-java-sdk-opensearch/src/main/java/com/amazonaws/services/opensearch/model/StartServiceSoftwareUpdateRequest.java