But be aware that the value might have been set because it is required. Changing it might violate audit policy for the system.
It would be better to review all related system values to determine if any additional changes should be made.
If QINACTITV is the cause, then QINACTMSGQ should also be reviewed to see if a message queue is named. If one is named, then it should be tested to see if any job is monitoring the queue. And if it's being monitored, then the application that does the monitoring should be used to control the timeouts rather changing QDSCJOBITV.
If QINACTMSGQ is set to *DSCJOB, then it should be changed to point to a new message queue that you create. You can then put programming in place to receive those messages. The messages can be tested to determine which job sent them. If they were sent by a valid operator job like yours, your program can ignore the messages. But if they are sent from jobs that should be disconnected, your program can issue the DSCJOB command for those jobs. They will then timeout at the appropriate disconnection interval.
What you are talking about is controlled by the System Value QINACTITV
This will sign off your session and job job is classified as DISCONNECTED.
When you sign back on, you should be right where you left off.
The next system value to look at is “QDSCJOBITV”
This value determines how long Disconnected jobs will be allowed to stay disconnected by the system ends the jobs.