This parameter specifies the interval at which the periodic background time scheduler runs. The background time scheduler is responsible for starting time base background jobs. you can get more information from RZ11.
1, if you want to reduce the value of this parameter, never to less than 30 seconds. for more information, please refer to following SAP Notes:
#90428 Time-controlled jobs start late
#386646 Event-controlled jobs start with a delay
#1508504 Load balancing in background processing
#1057255 Jobs remain in status 'ready'
-Time scheduler would run quite often, even if there are no batch jobs to start.
-With note 923228 we introduced a mechanism, that the time scheduler runs in shorter periods anyway, if there is much batch traffic in the system. So it is simply not necessary to set rdisp/btctime to a very small value.
2, if you want to set rdisp/btctime=0 to stop time scheduler running to restrict any time-driven jobs to be run in some special situation, please keep in mind that there are special circumstances, for more information, please refer to 1898924 - About rdisp/btctime=0 parameter.