If your publisher gives you a date then it should be okay to shout it out to everyone. When it comes to putting out your own books this can be a little more difficult. You upload the books at retailers and wait for them to go live.
Amazon and NookPress have a 12-48 hour window.
Smashwords and D2D distribute to retailers for you. I haven't used D2D, so I don't really know how they work. With Smashwords you go live on their site right away, but it can take a few days for it to show at the other online retailers.
ARe goes live right away too.
My plan is to load at Amazon, Nook, and Smashwords at the same time. Once I get word that the book is live at Amazon and Barnes and Noble I'll upload to ARe.
I'm guessing if you do pre-orders the files would all be there and ready to go. I haven't tried pre-orders so maybe someday I'll figure that out.
Before I focus on pre-orders I'm going to spend my time deciding how I want to set up my first box set. I'm going to be doing the first three books in the Heiresses In Aprons Series. I'll post more about this experiment over the next week.