As an editor, there is nothing as uncomfortable than a client who comes to me with a book release celebration date scheduled and planned, but they do not have an understanding of the editing process and timeline.
This can cause the author and everyone on their team to have to operate under a spirit of rush instead of a spirit of excellence. Operating under a spirit of rush means mistakes will be made.
Book a content/developmental editor at least two — three months in advance. I personally only take on a certain amount of editing projects at one time. I’d like to be able to plan for your project in advance to make sure I can dedicate the time needed. Some projects may require heavy editing, which means I'll have to dedicate even more time to that particular project.
The content editing phase typically takes three months depending on the length of the manuscript, and again, whether heavy editing will be required. I suggest first time authors, or those who have not studied the craft well enough to know the basic grammar/writing rules, allow a couple extra months to go back and forth with your editor.
But wait! Don’t book your release party just yet. You still have to get copy-editing done. I, too, am a copy-editor, but I do an entirely separate round of editing just for copy. If you work with a developmental editor who is not a copy-editor as well, you may have to do two or three rounds with your copy-editor. So, add another couple of months or so to the timeline.
The planning of the release party should never come before the planning of the production of your book. That’s totally putting the cart before the horse (BTW: If I was your editor, I’d never allow you to use such as lame cliché. Be original!).
So, if you are an author who already has your book release celebration engraved in stone on the calendar--venue paid for, among other things--my advice would be to either postpone the release or make it a soft launch in which you accept pre-orders only. Making your book available for pre-orders as well as having a full-blown pre-order campaign should be part of every authors' publishing process anyway.
It's never a good idea to release a book that has not been professionally edited . . . even if you do have a grammar program that you swear by. Remember, grammar programs may help you become a better writer, but they will never replace a human editor.