Can you wait a month to fill a cavity? The answer is: I don't know. If it's a small to medium-sized cavity, you might be able to wait a month. But, if it's deep and near the nerve, I would get it treated asap. Remember that while a cavity is a hole in the tooth, it's caused by bacteria! It's an infection and it will continue to progress and get worse with time. If it contacts the pulp ("nerve"), you'll need more than a filling. We're talking about a root canal and crown or extracting the tooth. I suggest you ask your dentist about the severity of your cavity and if you can wait. If you don't have a dentist, I'd visit one and have the tooth evaluated.
Hope this helps,
Steven Chamish, DDS