As a caucasian, non-israeli and non-jew, who travels to Israel through Ben Gurion around 1-3 times a year, let me add my experiences.
There are always lines, fairly long ones, leading up to the first check and x-raying of belongings. While you're slowly making your way to the x-ray machine, this is when you'll get your first interview. This process of standing in line and being interviewed will take from 10 to 30 minutes, if all goes well and you don't ring any bells.
After x-ray, there's another check of your hand luggage accompanied by the second interview, checking your answers from the first one; this will take 5 to 10 minutes, again provided all goes well.
Then you'll walk over to check-in, which are always chaotic since your average passenger leaving Ben Gurion has no concept of the idea of keeping an orderly que - but that happens in many other airports too. There'll be a bit of an interview, but it's the same as in most places around the world (did you pack your luggage yourself etc). Say 10 to 30 minutes, depending on class of travel.
Now you move off to have your passport checked, and a few more questions asked by the immigration officer. Add 5 to 15 minutes depending on length of ques.
Then it's off to have your carry-ons x-rayed, but before that there'll be another check of documents and perhaps a question or two. 10 to 20 minutes.
And, finally, you've passed security at Ben Gurion.
All times above reflect reality, but only if everything goes smoothly and you don't attract anything more than normal attention. It will take from 40 to 105 minutes. It's not for nothing you're requested to be at the airport 3 hours prior to STD!
My personal best, but only because I work for someone who knows someone and thus am able to apply for security pre-screening (it's just a document you fill out) AND is being escorted through the whole ordeal by someone who'll vouch for me, is 20 minutes.
If someone tells you it can be done, on average, in 20 to 30 minutes they're feeding you porkies.