Hi Jacky,
That timer is relevant only if EN_FAST_INITIAL_GPRS_ACCESS is disabled.
You should try to modify T_GCH_INACTIVITY instead, which would greatly reduce your GCH usage on ATER PS.
Ruel:
T_GCH_INACTIVITY > T_CANDIDATE_TBF_REALLOC (1 second) in all the cells of the BSS.
Best Regards,
Pix