Hello, welcome to HubPages!
I do believe that the character limit here is 10,000 characters within one hub, plenty for a short story. However, if you wanted to write a particularly long story, there is no rule or regulation as to how many hubs a day you can publish. What I'm saying is, you can separate your story into parts and publish all parts on the same day if you would like.
Feel free to ask any other question, and I look forward to your continued use of HubPages!