How to set Max Wait Time for Queue

I am not able to set the Max Wait Time for my queue in the GUI. So i was thinking to set the Max Wait Time in extensions_additional.conf by exten => 129,2,Queue(example_queue,tT,300). However there is no extensions_additional.conf in /etc/asterisk.
How do I set the max wait time?

If you are running FreePBX there has to be an extensions_additional.conf

You can’t make changes to that file anyway as FreePBX will overwrite it.

You make your changes to extensions_custom.conf, however I think that this setting is part of a macro.

MAX wait time is in version 2.11 of FreePBX, you did not mention your version