Also it is used in MSS in Implicit attaché
here some Printouts:
>>Implicit IMSI detach timer (min) = 485
x=240min or 4hours
>> IMPLICIT DEREGISTRATION: 012 HRS. 05 MIN
IF T3212=X THEN implicit Timer can be something like this = 2X+some min
this means, we give subscriber another chance to do periodic location Update if first time got failed.