I had the countdown going on ticketmaster.com on my computer and when it got to zero it said presale starts in 24 hours...but I also had it going on the TM app on my phone and that worked. Got 2 GA tickets for SJ in under two minutes.
Oh, and it did get a bit crowded once U2 came out but never claustrophobic. Our plan was to watch the mini set and beginning of TJT then moving back to take it all in but we ended up staying where we were the whole time. Here's a pic in the daylight during Mumford so you can see approx how far we were from main stage
I thought the sound was great and I really liked our spot - close enough to the B stage to see facial expressions but also nice and centered for the main stage portion with great views of the screens. Here's a pic of approx how close we were to the B stage (Adam was behind Bono and to the right a bit so seeing him was a bit tougher)
Not sure how helpful this is but Wednesday night in Santa Clara we got inside the venue around 6:15pm and were pretty much right near where you want to be - a little back from the B stage, pretty much in the center