Yes Steve, you can manually change it.
Here, shown changing to 15. DOnt go too low, or the Cell wont have a chance to get the call.
UC_540(config)#ephone-dn
UC_540(config-ephone-dn)#snr 203 delay 5 timeout 15 cfwd-noan 399
In the next release, we are talking about making that adjustable via CCA.
Steve