hey,
another question 
in my company I have queues with approx 8 agents. if 4 of them are away and have pressed the dnd button, nobody else should be able to press dnd. is it possible to implement this in freepbx?
additional it would be interesting to know, how many agents have pressed dnd and for how long…
I’m using freepbx 2.11 and asterisk 11.2.1
There is nothing in FreePBX to implement the ability to disable DND based on queue agents logged in or un-paused in a queue. Doing such would involve some customization to your system if that was exactly what you required. You would have to modify the dialplan that implements DND to check the number of members in a queue, which of course would be very specific to your setup. You would also have to make sure your phones are using server side DND and there are no places DND is getting set (such as User Portal, 3rd party applications, XML applications, etc.)
There are a lot of ‘knobs’ you can turn on Queues to get quite a variety of behavior if you have any control over changing how people do things.