Your speech is not something you want to leave to the last minute. This is how stress and nerves are able to take hold. I would recommend that you start thinking of what you want to say at least 2-3 months out. That doesn’t mean that you have the speech finalised then – you are just getting some ideas of how you want it sound and what you want to include. I would recommend having it finalised at least 2 weeks out from the wedding so that you can practice it a few times and be comfortable with everything you want to say.