Hi Richard,
I would like to mention that it is generally not a good idea to have many contacts within an automation process (for example on the waiting step) as it may have performance impacts. And further, there is unfortunately no direct support for such scenario.
If you have a scenario, where you would like to accumulate contacts and then send them all a newsletter at once, a better approach would be to subscribe them in the automation process only and then have the newsletter scheduler handle the sending.
Also, if you are planning on using similar scenario often, and you do not want to send a newsletter issue, but perform some other action, you can change some "contact status" in the automation process and then have a scheduled task perform the action for all such contacts.