What I sometime do at a quite small forum is to look at the /u page
Choosing today as a time span and sort by visits (like this) gives you a list of all users who visited today. The newest user will be the last one with one visit. Here this needs a lot of scrolling. The /about statistics show more than 500 active users in the past 24 hours and 36 sign-ups. That gives you an idea how far you have to scroll and how many new users you will find (Keep in mind maybe some of them were already deleted)
(try.discourse.org is an example with less active users. But the statistics there are less helpful)