user defined aging time of service-set

Dear Experts,

  I'm new in huawei firewall (USG). I've created a user defined service-set like below:

ip service-set web type object
service 0 protocol tcp destination-port 80
service 1 protocol tcp destination-port 2121

I've set aging time of this service-set like:

firewall session aging-time service-set web 1800

Now if I see the session table:

[SRG]display firewall session table verbose
17:59:54  2016/08/18
Current Total Sessions : 1
  tcp  VPN:public --> public
  Zone: trust--> untrust  TTL: 00:10:00  Left: 00:09:57
  Interface: GigabitEthernet0/0/1  NextHop: 192.168.2.2  MAC: 54-89-98-ac-65-7b
  <--packets:8 bytes:519   -->packets:9 bytes:410
  192.168.1.2:2058-->192.168.2.2:2121

TTL value is 10 mintues, which is default value of TCP.

I want to set my custom value 1800 in web service-set.

Please help me.

Best Regards

Banik