Indeed, the general guidance is to keep checking, as people cancel and then things open up, but you only know if you are in the system when it happens.
I did like Cyn but had a completely different experience. A 90-minute wait in Atlanta, but luckily I had a three-hour layover. It did get taken care of though, and I had my KTN when I walked away from the desk. Just to underline that you may not be so lucky as to get through in 5 minutes ! (Oh and I didn't get waved through anywhere — had to stand in line and do the regular entry immigration control, at which point after that was done, they allowed me to go to the desk to get in line for the Global Entry interview.)
(My previous trip arriving in Atlanta, the guy doing the interviews had just gone on break and they told me it would be 20 minutes or so before he would be back to start the interview — the interview itself is short, but then they have to run your fingerprints through a database and wait for any results to come back —so doing the whole thing takes a good 15 to 20 minutes in my experience. Anyway, I had a much shorter layover that time, so I was unable to wait for the interview and just had to go on.)