I was up around 1:30 am EST with our toddler and happened to stumble across the sale. I frantically got in 2 $200ish orders of some of the Ninjago, Minecraft, and the City sub. 2nd order included the JP T-Rex set. The large Ninjago Dragon and the JP Brachiosaurus sets were down to the last couple and sold out before I was able to complete the first order.
I got my toddler back to bed and moved on to deal with our fussy newborn (fun night!), and checked back around 2:30 and my entire 2nd order was cancelled. I don't know if it was some sort of fraud detection or if everything had legitimately sold out in the 5 minutes between order 1 and 2. I was able to place a small order at 2:30 for a couple of things that were still in stock, and when I got up with the newborn again at 5am pretty much everything was done.
Not sure when it went live - if it started at midnight EST then there was probably a fair amount of stuff in stock then, at least of the midrange sets that were selling out under my feet.