Instructions
This value is dependent on the conversion time, the type of measurement (current, voltage and resistance measurement) and the number of active channels.

The total conversion time determined (basic conversion time + additional conversion times) for a channel has to be multiplied by the number of active channels. This gives you the cycle time for a module. A signal must be present for at least this time to ensure that it is recognized as a process alarm.

The following manuals give information on the length of the basic conversion times of the various modules and on any additional conversion times that might have to be taken into account 
 

Modules	Manual	Entry ID
ET200M	SIMATIC S7-300 programmable logic controller, module data	8859629
ET200S	SIMATIC ET 200S distributed I/O system	1144348
ET 200iSP	SIMATIC ET 200iSP distributed I/O device	28930789
ET 200pro	SIMATIC ET 200pro distributed IO system	21210852
ET 200eco PN	SIMATIC ET 200eco PN distributed I/O device	29999018

If smoothing of the input signals has also been configured, the smoothing level which has been parameterized has to be taken into account. The smoothing levels (weak, medium and strong) are multiples of the cycle time and vary depending on the module used. 
The smoothing level attenuates the rise of an input signal. The specification in cycles indicates in how many cycles an input signal with 63% of its maximum value is recognized

Note
Refer to the manuals listed above to find out the number of cycles per smoothing level for your module.