I had difficulties too: I started at 5:02AM EST and got a Queue-it message that there were about 100 people in front of me. About a minute later, my turn came up and I selected my two tickets (50 showed as available for 5PM May 3). However, when I hit the next step I got a "Please Wait" message, which lasted several minutes. When it disappeared and I tried to proceed, I got the wait message again. This continued for about 15 minutes and I gave up and exited, deleted my browsing history, and restarted my computer. When I got back in the line was much longer (might have been upper 800s). After about 10 minutes I got into the sight and was able to select and purchase my tickets for May 3 without any technical issues. However, I snagged the 15:00 timeframe not the desired 17:00 slot (I was bleary eyed and a little rattled). Further, I found the checkout a little confusing, so note to future users: the donation is a two step process - select an amount and then check a check box to accept it; agree to terms by checking the somewhat discreet check box; and select the method of payment. And don't be intimidated by the bright red message that shows the time to finish ticking down.
I had performed the ticket process the last three Tuesdays in early hours and never got the Queue-it messages, so that was a surprise. I am happy to get the tickets on the day we wanted. And MANY THANKS to those responding to my questions as well as those of others in this forum.
Sorry for rambling. and Happy Travels to all.