When you get banned from a community for doing something inappropriate the ban can last anywhere from 1 hour, to 1 day, or even forever! It really depends on the severity of what you did to get banned.
If you were banned from a community, and feel that the decision was unfair, you should attempt to take that up with the staff of that community. In general, we will not override the community staff's decision to ban someone.
Remember, if you do not like the rules or staff of a community, you are always welcome to try visiting a different community, or you can even make your own community with your own set of rules.