Haneda airport will open up to international flights next month as Japan works to maintain Tokyo's status as an Asian travel hub. But it comes with a big catch for U.S. airlines that have been squeezed into the least convenient time slots.

Opening Haneda to international flights makes a lot of sense for travelers.

It's just a 20-minute monorail or cab ride from central Tokyo. Narita International, the capital's other airport, requires at least an hour train ride, and the trip can take more than two hours when traveling by car on clogged roads.