When it actually worked for me, I never waited more than 36 hours for approval, my record was 5 hours. Sadly I changed passports and now it no longer works, I will need to leave the country and return to get the online working again. :(
I have had 17 passports in the last 38 years, everyone changed because they were full. I have seen repeated posts where this should be possible but in my case the reality was they do not seem competent enough to do it.
Now if they could just tie their databases together so that you don't have to leave and reenter the country to get online 90 day reporting to work when you have just got a new passport !!!