As the specification askes to verify the timestamp in Part 6 Section 6.3 of the spec for security reasons, this sentence needs to be changed.
Creating a MantisIssue for Part 4.

The group felt that Part 4 should remove the word "Only" - the TimeStamp is also used for security

We added this sentence in Part 4 to make clear that a service request is NOT rejected because of a time difference and not synchronized clocks.
The sentence was added in OPC UA 1.02 (see Mantis issue 0001449)

We added this sentence since such test was in earlier versions of the CTT and the UA WG decided that such tests make no sense.

The text in OPC UA Part 6 - 6.3 is not very concrete. The only shall talks about a configuration parameter. There is no definition what an application (client or server) should do if it detects that the times are not synchronized.

As long as we do not have a general concept for time synchronization, we are not able to enforce such harsh behaviour like rejecting service requests. There should be a better way to indicate suceh a problem that "you are not longer able to talk to me".

Please assign this back to the CTT. No change in Part 4 since this sentence was added intentionally (see comment above with reference mantis issue 0001449)

It is sufficient to check that the request time stamp is non-zero.
At least as the test case is currently written.

That is not too difficult to implement on the server side.

But I agree that it would be very problematic when
more than just non-zero timestamp in the request header
has to be checked in the server.

We can only check the timestamp in the Service Request Header if we have mandatory time synchronization.

Agreed to no-fix in Dallas meeting.