Can an extension be tied directly to a trunk port?

Hello Guys,
I have a trixbox system with about 20 SIP extensions.
I also have 3 PSTN lines connected to a Grandstream GXW410x VOIP gateway. The GXW410x is Configured to function as a PEER gateway.
Is there a way to create a singular extension that is tied directly to the 3rd PSTN line on the GXW410x.
Basically i want that when PSTN line No. 1 is dialed after certain hours it is forwarded to PSTN line No. 3.

Any help will be greatly appreciated.