How long does it usually take for a book you're submitting to make the rounds to all the editors you plan on sending them to -- meaning, do you send it out to one editor at a time and the process can take a few years? Do you send them out five at a time, and the process take months? What's the average turnaround time until a book gets sold or probably isn't going to be?
There are two ways to submit projects - either exclusively to one editor at a time or simultaneously to various editors at different publishing houses. Fifteen years ago the industry standard was exclusive submissions, but that has since changed and multiple submissions are considered the norm (though certainly not the rule).
How many and which editors I submit to at any given time is a true trade secret. I determine a strategy based on the individual book and the potential publishers, and then I discuss this strategy with my client before submitting. I will say though that I almost always submit to at least three editors at any given time and have also submitted to up to twenty at once.
If or when I get a pass from an editor I may immediately send it out to another editor, or I may wait for more responses to see if they all describe the same problems about the project. If I submit a book to eight editors and they all pass with the same concern, then I might ask my client to revise before submitting elsewhere.
As for the average turnaround time before a book gets sold, there are too many factors for me to give an accurate answer. It depends on how many editors you can submit the project to (which depends on the genre), how long each editor takes to respond, whether the author decided to revise, how many editors express interest, whether I can conduct an auction, etc. I've sold some books just a few weeks after first submitting to editors, but I also once sold a book two and a half years after my initial submission.