1° Leave for how long?
The best way to know is to get started! Depending on your comfort and experience, you can adjust the duration of your bivouacs over time.
To begin with, a first family bivouac can last 1 to 2 nights, this already allows you to have a good overview. You will be able to plan what will await you if you decide to leave for longer. Especially if you are with children, it is best to be able to test the equipment and get them used to it.
Once you have gained experience, 2 to 4 nights allow you to explore more and feel a real break from the urban world. The most addicted will tell you that they can go away for entire weeks independently.
The main thing is to anticipate preparation and physical condition. Whether you are leaving for 1 night or 15 days, you must always consider the weather conditions. This seems obvious but always check the weather forecast before you go. Extreme conditions may limit the length of your stay.