In January I had the same question because the web site says indeed that it takes two days. I even wrote them an e-mail back then and they replied it was just one day, which proved to be correct. When the reply arrived, though, I had already booked my flight + hotel for an extra day in HCMC, so that was suboptimal, but Saigon was definitely worth staying another day. ;-)
I managed to register with a GMail address, but not with my regular e-mail addresses (domain patterns mydomain.name, mydomain.net), no idea why. No confirmation message yet. It seems I need to wait until I get a user name, is that correct?
, there is an app for 90 days report? Would you mind posting a link (Google Play store)? I read so many reports about people being unable to do it online because the web site rejects them without much explanation, just telling them to go to the immigration office. I tried by myself several times when I was on ED visa, just to see if I can get past the first data entry page, but never managed to.
So when my reports were due I always used the registered mail option. I had to wait 3-4 weeks for the receipt to arrive, but eventually it did both times. After I was safe, having sent the paper report, I also tried the online system each time within the 7 days window and was rejected every single time. So even though tedious, the registered mail option at least works and saves me the long way to + waiting time at Chaeng Wattana.