HOTLine over TIE (MCDN) ringback delay ?

[SL1M1]

This is the scenario, rather than a major config ie MultiTenant or PreTransLations

I've a group of 20 users leasing an office and wanting to be connected to their own PBX using their own Dialling Plans, cross connected off Main PBX CS1KM MG RLS 5.5 to CS1KE Rls 5.0

Offering transparency dialling through their own CS1KE (Linked via E1/SL1/MCDN Link)

Works fine but and set up as:-

Digital 3903's

Key 0 HOT D 4 xxxx (Route Access Code)
Key 1 SCR xxxx (DN)

CLS TLD
NCOS XX Deny/Allow

The only thing is I get a delay on ringback as and when off hook calling Extn's etc

Wondering is that interdigit timers from my side or their side ?
have tweaked in RDB with no joy ?

To make calls intersite via normal company dialling plan ie AC2 / Loc Codes I get ringback straight away

Any ideas guys ?

Cheers!!