It depends on dissertation requirement. It takes about a month or two to write a dissertation while our experts can do it under short deadlines as well.
Dissertation topic is what you have selected from your domain and the whole dissertation revolves around it while a title of your dissertation comes from your dissertation topic. It is not same at all.
Select your favourite domain and do some preliminary research on any one aspect of it. It will show you the most emerging issues, problems or gaps which can be easily turned into a topic. It will be good and interesting.