I never seem to "bonk," at least in ordinary riding (i.e., not a century)
I can go out for 2.5-3 hours with my heart rate averaging between 130-140, never take any nutrition, and just a little water, and it doesn't seem to bother me in the least.
However, on a century, I have never tried to push it, and generally do eat and drink as I go along. I would suppose that if I didn't, I would bonk, but I have never really tried, nor would I like to.
But, I read at times on this forum of people bonking after about an hour or so.
So, here is a little poll about bonking.