How can I stop planning my book excessively?

What I would do is limit the research to what you're actually going to need to know. This is a time travel book, if one of your characters is a ballet master do you really need to go into all the ins and outs of ballet? A couple of lines here and there should suffice. I think part of being a good writer isn't just researching...its knowing how to fake it. If one of your characters is a genius and you need something super smart for him to say, grab the Republic and have him quote a line or have him muse about Einstein's theory of relativity without going into detail. Your audience should only have to know that which is essential. If you bog them down with too much it can become boring and preachy. Character details are great but in the end, the question you need to ask yourself is this: Does it serve the story? If not than its filler.