With different manufacturers having different lead times, you will also want to leave enough time for alterations if required. Allow at least 3 weeks prior to the wedding.
Leave enough time for a second and possibly third fitting in case the dress still does not fit quite right. Many bridesmaids wait until less than a week before the wedding to pick up their dress only to find out it doesn't fit well and there’s not enough time to have it altered or sent back.
Looking for ideas and inspiration, view the Latest Bridesmaid Dress Designs