I think if you believe you'll need it to be tailored in any way, I would order it at least month in advance. A lot of people are last minute shoppers so if you order it too close to the date they might not be able to take it in or hem it up.
And, if you order it sooner than later, you can have it fit for perfection if anything changes along the way. I would get it at least mid March or end of March. 🙂