Ya know, that's a really good question at this point. What happens if you are using a third party script and that script tends to hang every now and then? I don't think that would cause any issues.
If that third party call were consistently latent, then you might be approaching that threshold of a poor load time. Heck, Google's GA has been responsible for delays in the past. Nowadays, they just throw a 404 if there is too much delay. I see them throughout the day.