Either way, they know there's going to massive seething. Possible riots and violent action by either side.
By delaying til the last possible second, they minimize this. Many people are going on a 3-4 day weekend if not on vacation all week. Lots of news coverage of the 250th and July 4th. Releasing it Tuesday gives only a day or two of bouncing and squeaking by the losing side before we hit the long weekend and the news cycle moves on. So they hope.
One thing I wonder: Is there any third option for the SC to kick the can down the road? Maybe punt to a lower court, do anything to keep things at status quo til Congress changes the law? Or is it a pure Constitutional question at this point where they must decide once and for all if the 14 Amendment is for slaves only and if Congress wants Magic Dirt they need a new law or Amendment?
I think one thing that precludes a ruling in Trump's favor is the Amendment writer's intent. They could have simply passed laws in 1868 giving former slaves citizenship, codifying representation, and tidying up Civil War debts and denying former CSA officers and officials the right to hold office (which was never enforced at all).
But they made an Amendment to the Constitution, which is a Big Deal. If the SC strikes down Birthright Citizenship, it basically renders an entire Amendment superfluous. So it could be argued that the writers of them Amendment really wanted to codify Magic Dirt.