Siemens Simatic S7-1500 Function Manual page 59

Cycle and response times of the S7-1500R/H redundant system
5.3 Influences on the cycle time of the S7-1500R/H redundant system
Minimum cycle time
It is often necessary to set a longer minimum cycle time for the CPUs of the S7-1500R/H
redundant system than for those of the non-redundant CPUs.
Recommendation: Select the minimum cycle time so that the cyclic program does not have
to be executed more frequently than your process requires. A longer minimum cycle time
that has been adapted to your process optimizes the entire system. The computing power
that is available per cycle by extending the minimum cycle time is then available for system
tasks such as communication.
Note
Too low cycle times
Cycle times that are too low can result in an excessive synchronization load and thus
terminate the SYNCUP.
58
Cycle and response times
Function Manual, 10/2018, A5E03461504-AD