1) Put the following into mpmissions/dayzOffline.nasdara/db/messages.xml:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<messages>
<message>
<delay>0</delay>
<repeat>0</repeat>
<deadline>5</deadline>
<onConnect>0</onConnect>
<shutdown>1</shutdown>
<text>#name will shutdown in #tmin minutes.</text>
</message>
</messages>
2) Verified from inside the container that the file is readable and contains exactly this content.
3) Start the server and wait more than 5 minutes after the mission has finished loading.