Very likely Callmanager is waiting for the interdigit timeout which is 10 seconds by default. You have a few options:
1. Let your users know that they will have to wait for the interdigit timeout when dialing 0 for the operator.
2. Create a 9.0 route pattern and set the Urgent Priority flag and configure the PreDot DDI.
3. Decrease the interdigit timeout as described in the following link.
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_tech_note09186a00800dab26.shtml
Hope this helps. If so, please rate the post.
Brandon