You can sign up both before or on the day of the event:
(i) Prior Sign Up
You can visit the universities page with the web widget to sign up to the Unibuddy platform, so that you have login details prior to the event.
You can find this page by a Google search, you can usually type the universities name followed by chat with us, for example "City University London Chat With Us" ; this should direct you to the Unibuddy widget to sign up.
(ii) On the day sign up
You can also wait until the day of the event to sign up via the event link. A page will be displayed via the link to either "Sign Up" or "Login".