rdisp/shutdown/longrunner_timeout is a SAP Parameter attribute which is used to control Max. time to wait for longrunner (e.g. batch jobs) during shutdown information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
This parameter defines how long the graceful shutdown waits for all
potentially long-running tasks, such as background jobs, to be ended
correctly.
The value 0 means that a timeout is not triggered when waiting.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.