Having at least three months to prepare for your First Dance is ideal. It's especially important if you haven't ever experienced what it's like to memorize dance steps. It takes a while to get the moves in your body. Once it's in there you can stop thinking "what comes next" and just enjoy dancing. It is a wonderful feeling! The anxiety about performing your First Dance drops away when you feel confident that you know the moves. I know this first hand from my 18 years of experience performing. The more prepared I am the more confident and excited I am about what I'm doing. This confidence is something your audience notices right away and they can't take their eyes off of you! You will own the dance floor!
It's just like anything else, the more you practice the better you will get, the more confident you will feel, the more connection you will have, and most importantly, it will be way more fun, which will make you happy, which is what we all want, right! So start practicing now and reap the benefits!