I was always under the impression that you can press your grapes at any point in the process. And the timing of the press is decided based on what you want to get out of it. Though the majority of my info comes from the old timers and their "old style winemaking", so I take it with a grain of salt.
And there's a million different variables that factor into the decision. And this is where a simple home winemakers knowledge (at least this home winemaker) falls short. All the what/where/when/why/how to press for specific results. Especially when factoring in desired ph and acids.
And then all those numbers go out the window when finding out many storebought wines I love have levels that would otherwise be way high/low.
So without a winemaker phd I plan to continue to keep it simple without trying to take on too much to comprehend at once. Which is more easily done making a full bodied dry red. Which basically allows me to push everything to the max before bacteria or oxygen could jeopardize anything. (My grandfather only made whites and always pressed the day after crushing) and I'll be Focusing more on how the must is looking and tasting, rather than counting days or being hung up on levels.
I'm just going to press at the end of primary until I acquire more knowledge (or need to troubleshoot a problem, which is where most of my knowledge is gained).
To avoid potential infections I've also been told about the process of crushing, adding pectin enzyme, and macerating for however long desired, and then pressing, all BEFORE AF. Which would allow the AF to take place without the skins and their higher susceptibility to infection. This way sounds great on paper, but I think I would need to understand the process much more before I ever attempted to do it. I am always looking to gain more knowledge, but sometimes learning one thing just brings up 10 new questions.