Launchd starts event 40 seconds later?
Two things:

Try placing your

&lt;string&gt;/Library/Preferences/SystemConfiguration&lt;/string&gt; 


inside an 

&lt;array&gt; 
&lt;/array&gt;


Additionally you may be able to watch to see when the change actually happens with the below command.

sudo fs_usage -f filesys | grep /Library/Preferences/SystemConfiguration