My mom had a crazy neighbor that came out to the fence and just stood there yelling at her dogs. I mean she is screaming "Shut up! Shut up!" over and over. Of course the dogs keep barking at her because she is screaming and making gestures like she wants to hit them. Then, the neighbor got a dog that barks a LOT! She hasn't been to the fence since!
I think people need to get over a few barks here and there but NOT continual barking. It is up to us to train our dogs or keep them in. Mine do bark when I take them out. I am with them so the barking is only a very few minutes. If there is some reason I cannot get them to stop barking right away, I take them back in. Like the neighbor who thinks it is okay for her cat to come sit on my fence post and tease the dogs into barking but will probably be the first to complain that my dogs bark! Still -- even when that happens, I take the dogs back in. I just don't want to give anyone the chance to complain.
I would say anything longer than 5-10 minutes and it is now a nuisance to others. If a new neighbor was complaining and you think you keep it to that. Tell them -- dogs are going to bark but you will ensure it is never for more than 5-10 minutes at a time. But that rule will go for any loud noise too!