The sign up process is completely automated with Instant Member - you don't have to do this manually.

Your user will get access immediately after payment, as payment processor will let Instant Member know that transaction processed succesfully.  You can also set automated 'Welcome Emails' to be sent to your new user and again this process does not require your direct involvement.

Equally if a subscriber fails to make a due payment their account will be automatically made inactive until payment is received.  The entire process is hands free.