I think you'll have a hard time trying to get the dog to stop barking on your own. Some beagles just love to find scents and bay. We very rarely ever let our dogs out before 6am and usually not later than 10 on the week days and 11 on the weekends. And they have to come right back in if they start baying. It's hard sometimes, though, when they find a rabbit scent, they get super excited.
But in all honesty, you're probably going to have to speak with your neighbors. If that doesn't work you can call animal control (at least here you can) and they'll give the people a warning. I don't know what they can actually do other than warn, but sometimes just the warning helps. good luck! Keep us posted!