Generally, people say 12 months or more. This is when a doctor will start looking into fertility issues. It's perfectly normal to take up to 12 months to conceive, after all, so six months, seven months, even ten months, it might seem like a long time but in terms of TTC it's actually not.
A 'long time' is different to different people. I didn't consider it a 'long time' until about 18 months had passed to be honest.
People who say "FINALLY I am pregnant after 4/5 months" are taking the piss a bit, though, when you consider that some people have been trying for ten years. After so long time starts blending into nothing, though. Five months feels like nothing to me, these days...