Assuming you are referring to an airing out of a bathroom that smells bad, the amount of time it takes for the bathroom to air out will depend on a few factors. These include the size of the bathroom, the ventilation in the bathroom, the type of odor, and the temperature and humidity levels.
In general, it will take a small bathroom with good ventilation and a light odor about 30 minutes to an hour to air out. A larger bathroom with poor ventilation and a strong odor can take several hours to a day to air out.
There are a few things you can do to help speed up the process. One is to open windows and doors to allow fresh air to circulate. Another is to use fans to help move the air around. Finally, you can try using natural odor absorbers like baking soda or charcoal to help remove the odor.