Multisite - Display a Link to Users Who Registered

I have a multisite setup. I'd like to display a link to users who registered within the past 30 days. The link should disappear after 30 days.

I tried to use this thread, but it didn't work. Luís also tried, but found it wasn't working for him as well.

Thread - http://wordpress.stackexchange.com/questions/143594/check-if-user-registered-more-than-a-month-ago

Any help would be greatly appreciated.

Thanks,
Chris