asterisk users - Oct 2010 - Asterisk 1.6 Overlap dialling timeout?

Hello,
I'm experimenting with Overlap Dialling in asterisk 1.6.
I've enabled this in sip.conf and on the SNOM 300 phone.

My problem is that asterisk dials out as soon as it matches an
extension without waiting to see if the user is going to type in more
digits.

Is there a way to set a timeout per channel or globally? 
I'd like Asterisk to wait for a few seconds once its found a match in
case the user needs to key in more digits.

Thank You.

Regards,
Veselin K