Restricting call duration on a specific trunk or context

Hi all,
I am relatively new with Asterisk, and I have a problem I don’t know how to solve.
I need to restrict outgoing calls on a particular trunk.
I am currently using the L(900000:60000) command in the General Settings page of the GUI, but that will make the restriction global, affecting all outgoing calls.
Is there any way to set up this restriction for a particular trunk or even for a specific context only?
I prefer to do things in the GUI if possible, but I know this has its limitations… If I need to do this in the configuration files please point me in the right direction and I will try to do it.
I’m currently using FreePBX

Thank you in advance!