It depends on what I've ordered, the restaurant I'm at, and how busy they are. I complained twice last year, both times when I ordered simple dishes. Usually if its simple and the place isn't mobbed, I'll complain after a half hour.

Once was at a Dave and Busters I complained after waiting 40 minutes for two pasta dishes. The second time was at a sports bar where I complained after waiting 45 minutes for a dozen wings and a meatball sub. The second place actually tried to tell me our order was "complicated", hence the wait.