As I understand from the definition of T3101, assignning a big value of such a timer will not increase the call setup time as you have said !
If T3101= 3sec that means if the mobile will not access the provided sddch traffic before 3 sec, the assigment message will end. This 3 sec is the maximun period to start call setup; it is not the real period;
In other words, if a mobile accessed the sdcch given via the AGCH in 1 sec, the timer will not stop him ! Anybody tell me if i am wrong