rdisp/noptime is a SAP Parameter attribute which is used to control Periodical nop for SAP work processes 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 .
Like rdisp/wp_auto_restart it is a timer given in seconds. Every noptime interval, the R/3 dispatcher sends a signal to the work processes that are not active at the time. Such a process checks the wp_auto_restart timer and if expired, gets restarted. For performance reasons ensure that the noptime value is higher than the value for wp_auto_restart.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.