Most often, you will begin working with a publicity firm four months in advance of your publication date. (ingramspark.com)
You need to set the stage and begin your visibility campaign well in advance of publication if you really want to reach a bigger audience and sell more books. (magnoliamedianetwork.com)
To do this, you need a very polished book, an imprint / press logo on the book, and to send out copies 3 months in advance of the publication date. (creativindie.com)