Overbearing In-Laws - How much time is enough?

Please don't get me wrong - I love my in-laws and we have a really good relationship but ever since I had my daughter, they (specifically my mother in law) want to spend every second with her. We see them at least 1-2 times a week (usually more) and they don't feel that that is enough. She usually babysits once a week when we go out to run errands and also just "pops" by without calling. I'm aware that I need to set some boundaries and that would be really easy to do if I had my husbands support but he seems to love it. He talks to each of his parents at least 2 times a day and if they want to ask us for dinner or anything - she calls my husband directly on his cell phone and talks to him about it. It's gotten to the point that I don't even answer the phone when she calls because she calls everyday. I work from home and am very busy throughout the day and don't have the time to talk. They plan everything that they do around what we are doing or going to do. How do I calmly get them to back off without ruffling any feathers and causing strain in any of our relationships?