My customer wants to be able to extend the length of time a call is on network hold, after pressing transfer and is busy looking up the number in the corporate directory. Not sure if there is a specific timer to alter this except possibly the hold reversion.?
The problem you are having is probably more related to the the off hook timeout not so much a hold timeout.
When you press transfer the system plays back dial tone waiting for someone to dial the first digits. This is controlled with the callmanager service parameter:
Off-hook to First Digit Timer, default is 15000 ms which gives the user 15 seconds.
Increase that and the system will wait longer for the user to search and select something from the directory.
One way to address this without changing any timer is having the user press the caller on hold, search the directory and place the call once they are connected use the Direct Transfer feature.