Login Verification

When using the Front End Login module, when the option “manual user verification” is selected, does an admin have to approve the login every single time a user logs in? Or does it just need to be approved the first time?
Basically I want to be able to make sure people accessing our courses are
a) verified clients of ours
b) not spammers / malicious users (as I’ve already had such people register and attempt to gain access)
c) enrolled in the correct courses before they start

But I don’t want to restrict users access to just times when I am available in the office.
Thanks for your help!