I think how they emphasize it has a lot to do with the individual testers. I believe they all tell the kids that it is a timed portion of the test, but some seem to emphasize it more than others.
For example when DS9 was tested at 7yo, I believe the psych told him that this portion of the test was timed and he should work as quickly as possible. For DS7, I believe the tester (a different psych) told him that it was timed, but with less emphasis to him about working as quickly as possible.
Of course, that's from my not-always-reliable recollection.
