While it's officially been 6am ET for online for quite some time, I always get up early in case it opens up a smidge early. It's always been 6am on the dot for me, but my dad has gotten in a little early several times. He's had several times where the site has flipped for him around 5:45-5:50. For this reason, if we're traveling together and have a hard-to-get ADR, we will both try. The other side of this is Disney can sometimes be slow to load all ADRs. We had one year where I booked everything that was available at 6am (which wasn't much) and then 20-30 minutes later, all of the times loaded and I rebooked everything. For another trip, they were having a glitch with Garden Grill and it was days before things were loaded for booking. I remember calling at 7am on the dot (this was back in the 180 days era) after my 6am online efforts failed and the girl that took my call had to tell me that nothing had been loaded and she had no ETA on when it would.