If a user does not open their Verification Email within 24 hours, the link will expire. Therefore, the user cannot verify their account and must create a new email and a new account or start the lengthy process of having an admin delete and re-add their account.
However, there is a solution!
If a user’s verification link becomes expired, a new link can be sent via the forgot password link at the login screen. Once this link to reset the password has been followed, the user's account will, in turn, verify itself.