They generally can't do a waiver until the AF is showing up on the statement (at least they couldn't for me), but you can try for a PC anytime.
Keep in mind that I was told "no" over and over (the last time in December) before being told "yes" in February, so don't get discouraged if you don't get it right away. If they don't give it to you now if it were me I would try back monthly (I was actually encouraged to do this once in a chat). 
*There is an exception with the permanent waiver... since it's 'permanent' you shouldn't have to wait until the AF is actually billed, but again I've only read of a couple of folks who were able to get that, and I believe one of those went through the EO. I would personally consider 'permanent' waivers an exception to the norm.