Ringgroup Destinations set to external DID

Hi Everyone

I have set the Destinations in Ring Group to some external DID's the timeout is not working. While if i set the Extension in Destination it works (I can see i leg_timeout=10 for extension in the dialstring while for DID it is not available).

I just want to know whether the timeout won't work with external DID's?

I have Master Version of FusionPBX 4.5.0 with Switch Version1.6.19.