rdisp/shutdown/max_time is a SAP Parameter attribute which is used to control Max. time for a graceful 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 .
You can use this parameter to set a maximum time for the execution of a
graceful shutdown. The default value 0 means that no restriction is
applied.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.