The test expects that a publish occurs within the fixed duration of the newly defined publishing interval immediately after a modification.
In our opinion, this assumption is not entirely correct.

The Unified Automation .NET SDK for example, calculates the timing of the next publish after a modification based on the elapsed time since the last publish (delta t) relative to the modification.

• If the new interval is shorter than the already elapsed time (delta t), the publish is sent immediately.
• If the new interval is longer, the elapsed time (delta t) is subtracted from the new interval, and the result determines the time until the next publish after the modification.
  After this first publish, the new publishing interval applies for all subsequent publishes.

It should be noted that the OPC UA specification is not entirely clear on this behavior, so the test cannot assume that a publish must occur strictly within the new interval immediately after a modification.

To properly verify that the modification was applied, the test should measure the time between the first and the second publish after the modify, rather than only the first publish.