I'm certain the link I posted can be used at anytime after you paid for your 6 month license. I just clicked on it and it opened a webpage inviting me to enter my registered email address to receive any bonuses linked to that email. I did that and received an email with another link in it, clicked on that and it took me to a new webpage that advised my new bonus is almost ready and to wait for a confirming email.
So the link works perfectly, you don't need to have MFPro open, to obtain your bonus subscription.