Since your version is no longer supported, there will be no fixes for this issue with Creo 3.
I would suggest upgrading your system to Creo 7 or 8 and see if PTC has fixed it already.
I am using Creo Parametric Release 3.0 and DatecodeM190
Please resolve the 7-10 second pause after performing the measurement command.
I have already set config.pro option clearance_triangulation to None.
But It hasn't improved.
I guess that I met situation when this problem was related to graphic card drivers.
Add following option into config.pro temporarily a test Creo behaviour.
If the problem disappears then it is related to graphic card drivers.
If you face this in all your models, the issue is probably related to graphic card used as @MartinHanak pointed out, and using graphics win32_gdi will allow you to degrade quality (getting rid from OpenGL Libraries) but gain in performance (and probably get rid from current issue upon access attempt of Measure User Interface).
Otherwsie, if you face it in the context of very big assemblies, we document this limitation and available workarounds (personnally preferring prehighlight no in such situations, unless you're confortable with Object/Action workflow, in other words, select first the references you want to measure with CTRL, and after that, access Measure UI) in resolution field of article 266555.