Definitely read Dirty Hair, Don't Care. But this is different for each person. I like to go a week personally. But, for some, the most they can do is every other day and some even choose to wash it every day. Everyday washing is normally for a finer or oily hair client. Some of my clients that have texture or trained their hair to do every other to every third day.
So, I answer this question different for each client. At most, every other day and try not to go much longer than a week. If you struggle with this, find yourself a good Dry Shampoo that works good for you. You also don't want to suffocate your hair follicle, which can create hair loss.