I am curious because in the future I am going to flip houses (renovate them) and then sell them for profit. So I need to know how long you have to own a house for before you can sell it.

In Michigan, it needs to stay in your name for 3 months. Another thing to think about… If you wait until the the taxes are due, you can claim any "green" upgrades you do to the house. New windows, roof, insulation, tank-less water heater… any energy efficient appliances or materials you purchase can be claimed on your taxes.