Nope, the edit grace period is never used for email notifications. Whenever you get a notification (due to a group mention, a user mention, a post in a watched topic, a quote or a direct reply), we enqueue an email to be sent in “SiteSetting.email_time_window_mins” which defaults to 10 minutes.
@saluzi I just checked and signup emails are not delayed. Can you check in the skipped emails log (/admin/email/skipped) if they were skipped?