Basically, the clay will dry out in room temperature within 24 hours or few days depends on weather in your home country, size and thickness of the model.
I did all my clay models - all sizes with my own ADC clay. I love the material so much. If you want to make your own clay you can check out my modeling clay recipes. But if you are not sure about it I would like to suggest you to buy ready-made air dry clay. (www.menzzitoy.com)