It's not so easy to turn-around watches to/from ADs within one month. To the extent that the watch has to cross Customs through countries, that often can take more than a week (each way) depending on the country and their Customs backlog. And even express shipping can take up to four days one way. That might leave a week for the actual service to be done!
Further, some watches require more time in repair than others, especially complicated ones. And after service, the testing can take longer than anticipated. I had an annual calendar (from another company) that needed a repair: the head watchmaker called me and explained that he kept the watch on his bench, and needed about three weeks to ascertain that, after his repair, all the functions changed correctly. Despite my impatience, he was right.
There are some companies, which will remain nameless here, which use very inexpensive movements. When then have a repair, they literally just exchange movements! This provides a quick turn-around, but I'm not sure it's what I'd want when I buy a watch for its movement as well as its looks.
Simply stated, a month turn-around is a great idea, but the implementation isn't so simple or practical in many instances.