Its fine to test, but not fair when it goes beyond 3.5 hrs. You should try to have checkboxes of you expectation, listen to what candidate say and limit it to 5 or ,,6 ques. If not that might prove that you are inefficient with your interview taking skills.
i said reading . they asked which one read at last?. i said half girlfriend. they asked how many page you had read. i said 120. how many novel?. i said 5. omg how old you are! 26 and you said reading is your hobby!