You can judge programmer's ability in 60 minutes. Can someone program? 60 minutes is way more than enough. How great of a programmer are they? You're going to need more than 60 minutes, unless already had a chance to look at their prior code base. What's difficult to judge is, are they organized? are they hard working? how do they handle stress? how's their communication and attitude? do they write great documentatio…
You answer in the affirmative, but then go on to clarify that you're excluding 95% of the job. I would simplify this to say "no, you can't".