The PROFINET Update Time of an IO Device is configurable individually depending on the application: typical values range from 1 to 128 ms in RT, and down to 250 us in IRT.

The Update Time is the refresh period for cyclic IO data exchanged between the Controller and a Device. The shorter the Update Time, the higher the network load: a slow sensor (e.g. temperature) is fine with 128 ms, a proximity sensor or actuator typically runs at 4-8 ms, and a motion drive is usually configured at 1 ms or below in IRT. Good practice is to size each device's Update Time to actual need in order to avoid network saturation and preserve overall determinism.

When in doubt, start with the device manufacturer's default Update Time; halving it doubles the bandwidth share of that device with no functional benefit if the application is not faster than the original value.