I ordered mine in March from the bridal boutique and it came in 4 months later. I had to have the initial try-on right away to see what all would need to be done. Fortunately it was a near perfect fit! I had a fitting in August and the final one the beginning of September for our October wedding. They did one minor thing after the August fitting and the September one was just to see it all "done."
But my seamstress said if I'm the type to fluctuate in my weight she would do another fitting closer to the wedding date. I've been the same weight for years so that wasn't a concern for me, but it might be something to consider if you think you'll lose or gain due to stress or a diet.