If you want you can increase the FNA Timer Clusterwide. Here's the detail:
CUCM Addminstration page:
System-->Service Parameter-->"Select your Server and the Service from the drop down menu"-->"Clusterwide Parameters (Feature - Forward)"--> Forward No Answer;
Default: 12
Minimum: 1
Maximum: 300
Unit: sec
Make sure the value that is specified in this parameter is less than the value that is specified in the T301 Timer parameter. If the value in the Forward No Answer Timer parameter is greater than the value that is specified in the T301 Timer parameter, the call does not get forwarded and the caller receives a busy signal. Note that FNA Timer is in "Sec" and the T301 is in "msec"
MK